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rfc:rfc2353

Network Working Group G. Dudley Request for Comments: 2353 IBM Category: Informational May 1998

                      APPN/HPR in IP Networks
         APPN Implementers' Workshop Closed Pages Document

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (1998).  All Rights Reserved.

Table of Contents

 1.0  Introduction  . . . . . . . . . . . . . . . . . . . . . . .   2
 1.1  Requirements  . . . . . . . . . . . . . . . . . . . . . . .   3
 2.0  IP as a Data Link Control (DLC) for HPR   . . . . . . . . .   3
 2.1  Use of UDP and IP   . . . . . . . . . . . . . . . . . . . .   4
 2.2  Node Structure  . . . . . . . . . . . . . . . . . . . . . .   5
 2.3  Logical Link Control (LLC) Used for IP  . . . . . . . . . .   8
   2.3.1  LDLC Liveness   . . . . . . . . . . . . . . . . . . . .   8
     2.3.1.1  Option to Reduce Liveness Traffic   . . . . . . . .   9
 2.4  IP Port Activation  . . . . . . . . . . . . . . . . . . . .  10
   2.4.1  Maximum BTU Sizes for HPR/IP  . . . . . . . . . . . . .  12
 2.5  IP Transmission Groups (TGs)  . . . . . . . . . . . . . . .  12
   2.5.1  Regular TGs   . . . . . . . . . . . . . . . . . . . . .  12
     2.5.1.1  Limited Resources and Auto-Activation   . . . . . .  19
   2.5.2  IP Connection Networks  . . . . . . . . . . . . . . . .  19
     2.5.2.1  Establishing IP Connection Networks   . . . . . . .  20
     2.5.2.2  IP Connection Network Parameters  . . . . . . . . .  22
     2.5.2.3  Sharing of TGs  . . . . . . . . . . . . . . . . . .  24
     2.5.2.4  Minimizing RSCV Length  . . . . . . . . . . . . . .  25
   2.5.3  XID Changes   . . . . . . . . . . . . . . . . . . . . .  26
   2.5.4  Unsuccessful IP Link Activation   . . . . . . . . . . .  30
 2.6  IP Throughput Characteristics   . . . . . . . . . . . . . .  34
   2.6.1  IP Prioritization   . . . . . . . . . . . . . . . . . .  34
   2.6.2  APPN Transmission Priority and COS  . . . . . . . . . .  36
   2.6.3  Default TG Characteristics  . . . . . . . . . . . . . .  36
   2.6.4  SNA-Defined COS Tables  . . . . . . . . . . . . . . . .  38
   2.6.5  Route Setup over HPR/IP links   . . . . . . . . . . . .  39
   2.6.6  Access Link Queueing  . . . . . . . . . . . . . . . . .  39
 2.7  Port Link Activation Limits   . . . . . . . . . . . . . . .  40

Dudley Informational [Page 1] RFC 2353 APPN/HPR in IP Networks May 1998

 2.8  Network Management  . . . . . . . . . . . . . . . . . . . .  40
 2.9  IPv4-to-IPv6 Migration  . . . . . . . . . . . . . . . . . .  41
 3.0  References  . . . . . . . . . . . . . . . . . . . . . . . .  42
 4.0  Security Considerations   . . . . . . . . . . . . . . . . .  43
 5.0  Author's Address  . . . . . . . . . . . . . . . . . . . . .  44
 6.0  Appendix - Packet Format  . . . . . . . . . . . . . . . . .  45
 6.1  HPR Use of IP Formats   . . . . . . . . . . . . . . . . . .  45
   6.1.1  IP Format for LLC Commands and Responses  . . . . . . .  45
   6.1.2  IP Format for NLPs in UI Frames   . . . . . . . . . . .  46
 7.0  Full Copyright Statement  . . . . . . . . . . . . . . . . .  48

1.0 Introduction

 The APPN Implementers' Workshop (AIW) is an industry-wide consortium
 of networking vendors that develops Advanced Peer-to-Peer
 Networking(R) (APPN(R)) standards and other standards related to
 Systems Network Architecture (SNA), and facilitates high quality,
 fully interoperable APPN and SNA internetworking products.  The AIW
 approved Closed Pages (CP) status for the architecture in this
 document on December 2, 1997, and, as a result, the architecture was
 added to the AIW architecture of record.  A CP-level document is
 sufficiently detailed that implementing products will be able to
 interoperate; it contains a clear and complete specification of all
 necessary changes to the architecture of record.  However, the AIW
 has procedures by which the architecture may be modified, and the AIW
 is open to suggestions from the internet community.
 The architecture for APPN nodes is specified in "Systems Network
 Architecture Advanced Peer-to-Peer Networking Architecture Reference"
 [1].  A set of APPN enhancements for High Performance Routing (HPR)
 is specified in "Systems Network Architecture Advanced Peer-to-Peer
 Networking High Performance Routing Architecture Reference, Version
 3.0" [2].  The formats associated with these architectures are
 specified in "Systems Network Architecture Formats" [3].  This memo
 assumes the reader is familiar with these specifications.
 This memo defines a method with which HPR nodes can use IP networks
 for communication, and the enhancements to APPN required by this
 method.  This memo also describes an option set that allows the use
 of the APPN connection network model to allow HPR nodes to use IP
 networks for communication without having to predefine link
 connections.
 (R) 'Advanced Peer-to-Peer Networking' and 'APPN' are trademarks of
 the IBM Corporation.

Dudley Informational [Page 2] RFC 2353 APPN/HPR in IP Networks May 1998

1.1 Requirements

 The following are the requirements for the architecture specified in
 this memo:
 1.  Facilitate APPN product interoperation in IP networks by
     documenting agreements such as the choice of the logical link
     control (LLC).
 2.  Reduce system definition (e.g., by extending the connection
     network model to IP networks) -- Connection network support is an
     optional function.
 3.  Use class of service (COS) to retain existing path selection and
     transmission priority services in IP networks; extend
     transmission priority function to include IP networks.
 4.  Allow customers the flexibility to design their networks for low
     cost and high performance.
 5.  Use HPR functions to improve both availability and scalability
     over existing integration techniques such as Data Link Switching
     (DLSw) which is specified in RFC 1795 [4] and RFC 2166 [5].

2.0 IP as a Data Link Control (DLC) for HPR

 This memo specifies the use of IP and UDP as a new DLC that can be
 supported by APPN nodes with the three HPR option sets:  HPR (option
 set 1400), Rapid Transport Protocol (RTP) (option set 1401), and
 Control Flows over RTP (option set 1402).  Logical Data Link Control
 (LDLC) Support (option set 2006) is also a prerequisite.
 RTP is a connection-oriented, full-duplex protocol designed to
 transport data in high-speed networks.  HPR uses RTP connections to
 transport SNA session traffic.  RTP provides reliability (i.e., error
 recovery via selective retransmission), in-order delivery (i.e., a
 first-in-first-out [FIFO] service provided by resequencing data that
 arrives out of order), and adaptive rate-based (ARB) flow/congestion
 control. Because RTP provides these functions on an end-to-end basis,
 it eliminates the need for these functions on the link level along
 the path of the connection.  The result is improved overall
 performance for HPR.  For a more complete description of RTP, see
 Appendix F of [2].
 This new DLC (referred to as the native IP DLC) allows customers to
 take advantage of APPN/HPR functions such as class of service (COS)
 and ARB flow/congestion control in the IP environment.  HPR links
 established over the native IP DLC are referred to as HPR/IP links.

Dudley Informational [Page 3] RFC 2353 APPN/HPR in IP Networks May 1998

 The following sections describe in detail the considerations and
 enhancements associated with the native IP DLC.

2.1 Use of UDP and IP

 The native IP DLC will use the User Datagram Protocol (UDP) defined
 in RFC 768 [6] and the Internet Protocol (IP) version 4 defined in
 RFC 791 [7].
 Typically, access to UDP is provided by a sockets API.  UDP provides
 an unreliable connectionless delivery service using IP to transport
 messages between nodes.  UDP has the ability to distinguish among
 multiple destinations within a given node, and allows port-number-
 based prioritization in the IP network.  UDP provides detection of
 corrupted packets, a function required by HPR.  Higher-layer
 protocols such as HPR are responsible for handling problems of
 message loss, duplication, delay, out-of-order delivery, and loss of
 connectivity.  UDP is adequate because HPR uses RTP to provide end-
 to-end error recovery and in-order delivery; in addition, LDLC
 detects loss of connectivity.  The Transmission Control Protocol
 (TCP) was not chosen for the native IP DLC because the additional
 services provided by TCP such as error recovery are not needed.
 Furthermore, the termination of TCP connections would require
 additional node resources (control blocks, buffers, timers, and
 retransmit queues) and would, thereby, reduce the scalability of the
 design.
 The UDP header has four two-byte fields.  The UDP Destination Port is
 a 16-bit field that contains the UDP protocol port number used to
 demultiplex datagrams at the destination.  The UDP Source Port is a
 16-bit field that contains the UDP protocol port number that
 specifies the port to which replies should be sent when other
 information is not available.  A zero setting indicates that no
 source port number information is being provided.  When used with the
 native IP DLC, this field is not used to convey a port number for
 replies; moreover, the zero setting is not used.  IANA has registered
 port numbers 12000 through 12004 for use in these two fields by the
 native IP DLC; use of these port numbers allows prioritization in the
 IP network.  For more details of the use of these fields, see 2.6.1,
 "IP Prioritization" on page 28.
 The UDP Checksum is a 16-bit optional field that provides coverage of
 the UDP header and the user data; it also provides coverage of a
 pseudo-header that contains the source and destination IP addresses.
 The UDP checksum is used to guarantee that the data has arrived
 intact at the intended receiver.  When the UDP checksum is set to

Dudley Informational [Page 4] RFC 2353 APPN/HPR in IP Networks May 1998

 zero, it indicates that the checksum was not calculated and should
 not be checked by the receiver.  Use of the checksum is recommended
 for use with the native IP DLC.
 IP provides an unreliable, connectionless delivery mechanism.  The IP
 protocol defines the basic unit of data transfer through the IP
 network, and performs the routing function (i.e., choosing the path
 over which data will be sent).  In addition, IP characterizes how
 "hosts" and "gateways" should process packets, the circumstances
 under which error messages are generated, and the conditions under
 which packets are discarded.  An IP version 4 header contains an 8-
 bit Type of Service field that specifies how the datagram should be
 handled.  As defined in RFC 1349 [8], the type-of-service byte
 contains two defined fields.  The 3-bit precedence field allows
 senders to indicate the priority of each datagram.  The 4-bit type of
 service field indicates how the network should make tradeoffs between
 throughput, delay, reliability, and cost.  The 8-bit Protocol field
 specifies which higher-level protocol created the datagram.  When
 used with the native IP DLC, this field is set to 17 which indicates
 the higher-layer protocol is UDP.

2.2 Node Structure

 Figure 1 on page 6 shows a possible node functional decomposition for
 transport of HPR traffic across an IP network.  There will be
 variations in different platforms based on platform characteristics.
 The native IP DLC includes a DLC manager, one LDLC component for each
 link, and a link demultiplexor.  Because UDP is a connectionless
 delivery service, there is no need for HPR to activate and deactivate
 lower-level connections.
 The DLC manager activates and deactivates a link demultiplexor for
 each port and an instance of LDLC for each link established in an IP
 network.  Multiple links (e.g., one defined link and one dynamic link
 for connection network traffic) may be established between a pair of
 IP addresses.  Each link is identified by the source and destination
 IP addresses in the IP header and the source and destination service
 access point (SAP) addresses in the IEEE 802.2 LLC header (see 6.0,
 "Appendix - Packet Format" on page 37); the link demultiplexor passes
 incoming packets to the correct instance of LDLC based on these
 identifiers.  Moreover, the IP address pair associated with an active
 link and used in the IP header may not change.
 LDLC also provides other functions (for example, reliable delivery of
 Exchange Identification [XID] commands).  Error recovery for HPR RTP
 packets is provided by the protocols between the RTP endpoints.

Dudley Informational [Page 5] RFC 2353 APPN/HPR in IP Networks May 1998

 The network control layer (NCL) uses the automatic network routing
 (ANR) information in the HPR network header to either pass incoming
 packets to RTP or an outgoing link.
 All components are shown as single entities, but the number of
 logical instances of each is as follows:
 o   DLC manager -- 1 per node
 o   LDLC -- 1 per link
 o   Link demultiplexor -- 1 per port
 o   NCL -- 1 per node (or 1 per port for efficiency)
 o   RTP -- 1 per RTP connection
 o   UDP -- 1 per port
 o   IP -- 1 per port
 Products are free to implement other structures.  Products
 implementing other structures will need to make the appropriate
 modifications to the algorithms and protocol boundaries shown in this
 document.

Dudley Informational [Page 6] RFC 2353 APPN/HPR in IP Networks May 1998

  1. ——————————————————————-
  1. *
  • ————-* *——-* |

|Configuration| | Path | |

    |   Services  |       |Control|     |
    *-------------*       *-------*     |
          A A                 A         |
          | |                 |         |
          | |                 V         |
          | |              *-----*      | APPN/HPR
          | |              | RTP |      |
          | |              *-----*      |
          | |                 A         |
          | |                 |         |
          | |                 V         |
          | |              *-----*      |
          | |              | NCL |      |
          | |              *-----*      |
          | *------------*    A        -*
          |              |    |
          V              V    V        -*
        *---------*    *---------*      |
        |   DLC   |--->|  LDLC   |      |
        | manager |    |         |      |
        *---------*    *---------*      |
             |              A |         | IP DLC
             *-----------*  | *----*    |
                         V  |      |    |
                       *---------* |    |
                       |  LINK   | |    |
                       |  DEMUX  | |    |
                       *---------* |    |
                            A    *-*   -*
                            |    |
                            |    V
                         *---------*
                         |   UDP   |
                         *---------*
                              A
                              |
                              V
                         *---------*
                         |   IP    |
                         *---------*
  1. ——————————————————————-

Figure 1. HPR/IP Node Structure

Dudley Informational [Page 7] RFC 2353 APPN/HPR in IP Networks May 1998

2.3 Logical Link Control (LLC) Used for IP

 Logical Data Link Control (LDLC) is used by the native IP DLC.  LDLC
 is defined in [2].  LDLC uses a subset of the services defined by
 IEEE 802.2 LLC type 2 (LLC2).  LDLC uses only the TEST, XID, DISC,
 DM, and UI frames.
 LDLC was defined to be used in conjunction with HPR (with the HPR
 Control Flows over RTP option set 1402) over reliable links that do
 not require link-level error recovery.  Most frame loss in IP
 networks (and the underlying frame networks) is due to congestion,
 not problems with the facilities.  When LDLC is used on a link, no
 link-level error recovery is available; as a result, only RTP traffic
 is supported by the native IP DLC.  Using LDLC eliminates the need
 for LLC2 and its associated cost (adapter storage, longer path
 length, etc.).

2.3.1 LDLC Liveness

 LDLC liveness (using the LDLC TEST command and response) is required
 when the underlying subnetwork does not provide notification of
 connection outage.  Because UDP is connectionless, it does not
 provide outage notification; as a result, LDLC liveness is required
 for HPR/IP links.
 Liveness should be sent periodically on active links except as
 described in the following subsection when the option to reduce
 liveness traffic is implemented.  The default liveness timer period
 is 10 seconds.  When the defaults for the liveness timer and retry
 timer (15 seconds) are used, the period between liveness tests is
 smaller than the time required to detect failure (retry count
 multiplied by retry timer period) and may be smaller than the time
 for liveness to complete successfully (on the order of round-trip
 delay).  When liveness is implemented as specified in the LDLC
 finite-state machine (see [2]) this is not a problem because the
 liveness protocol works as follows:  The liveness timer is for a
 single link.  The timer is started when the link is first activated
 and each time a liveness test completes successfully.  When the timer
 expires, a liveness test is performed.  When the link is operational,
 the period between liveness tests is on the order of the liveness
 timer period plus the round-trip delay.
 For each implementation, it is necessary to check if the liveness
 protocol will work in a satisfactory manner with the default settings
 for the liveness and retry timers.  If, for example, the liveness
 timer is restarted immediately upon expiration, then a different
 default for the liveness timer should be used.

Dudley Informational [Page 8] RFC 2353 APPN/HPR in IP Networks May 1998

2.3.1.1 Option to Reduce Liveness Traffic

 In some environments, it is advantageous to reduce the amount of
 liveness traffic when the link is otherwise idle.  (For example, this
 could allow underlying facilities to be temporarily deactivated when
 not needed.)  As an option, implementations may choose not to send
 liveness when the link is idle (i.e., when data was neither sent nor
 received over the link while the liveness timer was running).  (If
 the implementation is not aware of whether data has been received,
 liveness testing may be stopped while data is not being sent.)
 However, the RTP connections also have a liveness mechanism which
 will generate traffic.  Some implementations of RTP will allow
 setting a large value for the ALIVE timer, thus reducing the amount
 of RTP liveness traffic.
 If LDLC liveness is turned off while the link is idle, one side of
 the link may detect a link failure much earlier than the other.  This
 can cause the following problems:
 o   If a node that is aware of a link failure attempts to reactivate
     the link, the partner node (unaware of the link failure) may
     reject the activation as an unsupported parallel link between the
     two ports.
 o   If a node that is unaware of an earlier link failure sends data
     (including new session activations) on the link, it may be
     discarded by a node that detected the earlier failure and
     deactivated the link.  As a result, session activations would
     fail.
 The mechanisms described below can be used to remedy these problems.
 These mechanisms are needed only in a node not sending liveness when
 the link is idle; thus, they would not be required of a node not
 implementing this option that just happened to be adjacent to a node
 implementing the option.
 o   (Mandatory unless the node supports multiple active defined links
     between a pair of HPR/IP ports and supports multiple active
     dynamic links between a pair of HPR/IP ports.)  Anytime a node
     rejects the activation of an HPR/IP link as an unsupported
     parallel link between a pair of HPR/IP ports (sense data
     X'10160045' or X'10160046'), it should perform liveness on any
     active link between the two ports that is using a different SAP
     pair.  Thus, if the activation was not for a parallel link but
     rather was a reactivation because one of these active links had
     failed, the failed link will be detected.  (If the SAP pair for
     the link being activated matches the SAP pair for an active link,
     a liveness test would succeed because the adjacent node would

Dudley Informational [Page 9] RFC 2353 APPN/HPR in IP Networks May 1998

     respond for the link being activated.)  A simple way to implement
     this function is for LDLC, upon receiving an activation XID, to
     run liveness on all active links with a matching IP address pair
     and a different SAP pair.
 o   (Mandatory) Anytime a node receives an activation XID with an IP
     address pair and a SAP pair that match those of an active link,
     it should deactivate the active link and allow it to be
     reestablished.  A timer is required to prevent stray XIDs from
     deactivating an active link.
 o   (Recommended) A node should attempt to reactivate an HPR/IP link
     before acting on an LDLC-detected failure.  This mechanism is
     helpful in preventing session activation failures in scenarios
     where the other side detected a link failure earlier, but the
     network has recovered.

2.4 IP Port Activation

 The node operator (NO) creates a native IP DLC by issuing
 DEFINE_DLC(RQ) (containing customer-configured parameters) and
 START_DLC(RQ) commands to the node operator facility (NOF).  NOF, in
 turn, passes DEFINE_DLC(RQ) and START_DLC(RQ) signals to
 configuration services (CS), and CS creates the DLC manager.  Then,
 the node operator can define a port by issuing DEFINE_PORT(RQ) (also
 containing customer-configured parameters) to NOF with NOF passing
 the associated signal to CS.
 A node with adapters attached to multiple IP subnetworks may
 represent the multiple adapters as a single HPR/IP port.  However, in
 that case, the node associates a single IP address with that port.
 RFC 1122 [9] requires that a node with multiple adapters be able to
 use the same source IP address on outgoing UDP packets regardless of
 the adapter used for transmission.

Dudley Informational [Page 10] RFC 2353 APPN/HPR in IP Networks May 1998

  • ———————————————-*

| NOF CS DLC |

  • ———————————————-*

. DEFINE_DLC(RQ) .

 1     o----------------->o
       . DEFINE_DLC(RSP)  |
 2     o<-----------------*
       . START_DLC(RQ)    .      create
 3     o----------------->o------------------->o
       . START_DLC(RSP)   |                    .
 4     o<-----------------*                    .
       . DEFINE_PORT(RQ)  .                    .
 5     o----------------->o                    .
       . DEFINE_PORT(RSP) |                    .
 6     o<-----------------*                    .
           Figure 2. IP Port Activation
 The following parameters are received in DEFINE_PORT(RQ):
 o   Port name
 o   DLC name
 o   Port type (if IP connection networks are supported, set to shared
     access transport facility [SATF]; otherwise, set to switched)
 o   Link station role (set to negotiable)
 o   Maximum receive BTU size (default is 1461 [1492 less an allowance
     for the IP, UDP, and LLC headers])
 o   Maximum send BTU size (default is 1461 [1492 less an allowance
     for the IP, UDP, and LLC headers])
 o   Link activation limits (total, inbound, and outbound)
 o   IPv4 supported (set to yes)
 o   The local IPv4 address (required if IPv4 is supported)
 o   IPv6 supported (set to no; may be set to yes in the future; see
     2.9, "IPv4-to-IPv6 Migration" on page 35)
 o   The local IPv6 address (required if IPv6 is supported)
 o   Retry count for LDLC (default is 3)

Dudley Informational [Page 11] RFC 2353 APPN/HPR in IP Networks May 1998

 o   Retry timer period for LDLC (default is 15 seconds; a smaller
     value such as 10 seconds can be used for a campus network)
 o   LDLC liveness timer period (default is 10 seconds; see 2.3.1,
     "LDLC Liveness" on page 7)
 o   IP precedence (the setting of the 3-bit field within the Type of
     Service byte of the IP header for the LLC commands such as XID
     and for each of the APPN transmission priorities; the defaults
     are given in 2.6.1, "IP Prioritization" on page 28.)

2.4.1 Maximum BTU Sizes for HPR/IP

 When IP datagrams are larger than the underlying physical links
 support, IP performs fragmentation.  When HPR/IP links are
 established, the default maximum basic transmission unit (BTU) sizes
 are 1461 bytes, which corresponds to the typical IP maximum
 transmission unit (MTU) size of 1492 bytes supported by routers on
 token-ring networks.  1461 is 1492 less 20 bytes for the IP header, 8
 bytes for the UDP header, and 3 bytes for the IEEE 802.2 LLC header.
 The IP header is larger than 20 bytes when optional fields are
 included; smaller maximum BTU sizes should be configured if optional
 IP header fields are used in the IP network.  For IPv6, the default
 is reduced to 1441 bytes to allow for the typical IPv6 header size of
 40 bytes.  Smaller maximum BTU sizes (but not less than 768) should
 be used to avoid fragmentation when necessary.  Larger BTU sizes
 should be used to improve performance when the customer's IP network
 supports a sufficiently large IP MTU size.  The maximum receive and
 send BTU sizes are passed to CS in DEFINE_PORT(RQ).  These maximum
 BTU sizes can be overridden in DEFINE_CN_TG(RQ) or DEFINE_LS(RQ).
 The Flags field in the IP header should be set to allow
 fragmentation.  Some products will not be able to control the setting
 of the bit allowing fragmentation; in that case, fragmentation will
 most likely be allowed.  Although fragmentation is slow and prevents
 prioritization based on UDP port numbers, it does allow connectivity
 across paths with small MTU sizes.

2.5 IP Transmission Groups (TGs)

2.5.1 Regular TGs

 Regular HPR TGs may be established in IP networks using the native IP
 DLC architecture.  Each of these TGs is composed of one or more
 HPR/IP links.  Configuration services (CS) identifies the TG with the
 destination control point (CP) name and TG number; the destination CP

Dudley Informational [Page 12] RFC 2353 APPN/HPR in IP Networks May 1998

 name may be configured or learned via XID, and the TG number, which
 may be configured, is negotiated via XID.  For auto-activatable
 links, the destination CP name and TG number must be configured.
 When multiple links (dynamic or defined) are established between a
 pair of IP ports (each associated with a single IP address), an
 incoming packet can be mapped to its associated link using the IP
 address pair and the service access point (SAP) address pair.  If a
 node receives an activation XID for a defined link with an IP address
 pair and a SAP pair that are the same as for an active defined link,
 that node can assume that the link has failed and that the partner
 node is reactivating the link.  In such a case as an optimization,
 the node receiving the XID can take down the active link and allow
 the link to be reestablished in the IP network.  Because UDP packets
 can arrive out of order, implementation of this optimization requires
 the use of a timer to prevent a stray XID from deactivating an active
 link.
 Support for multiple defined links between a pair of HPR/IP ports is
 optional.  There is currently no value in defining multiple HPR/IP
 links between a pair of ports.  In the future if HPR/IP support for
 the Resource ReSerVation Protocol (RSVP) [10] is defined, it may be
 advantageous to define such parallel links to segregate traffic by
 COS on RSVP "sessions."  Using RSVP, HPR would be able to reserve
 bandwidth in IP networks.  An HPR logical link would be mapped to an
 RSVP "session" that would likely be identified by either a specific
 application-provided UDP port number or a dynamically-assigned UDP
 port number.
 When multiple defined HPR/IP links between ports are not supported,
 an incoming activation for a defined HPR/IP link may be rejected with
 sense data X'10160045' if an active defined HPR/IP link already
 exists between the ports.  If the SAP pair in the activation XID
 matches the SAP pair for the existing link, the optimization
 described above may be used instead.
 If parallel defined HPR/IP links between ports are not supported, an
 incoming activation XID is mapped to the defined link station (if it
 exists) associated with the port on the adjacent node using the
 source IP address in the incoming activation XID.  This source IP
 address should be the same as the destination IP address associated
 with the matching defined link station.  (They may not be the same if
 the adjacent node has multiple IP addresses, and the configuration
 was not coordinated correctly.)
 If parallel HPR/IP links between ports are supported, multiple
 defined link stations may be associated with the port on the adjacent
 node.  In that case, predefined TG numbers (see "Partitioning the TG

Dudley Informational [Page 13] RFC 2353 APPN/HPR in IP Networks May 1998

 Number Space" in Chapter 9 Configuration Services of [1]) may be used
 to map the XID to a specific link station.  However, because the same
 TG characteristics may be used for all HPR/IP links between a given
 pair of ports, all the link stations associated with the port in the
 adjacent node should be equivalent; as a result, TG number
 negotiation using negotiable TG numbers may be used.
 In the future, if multiple HPR/IP links with different
 characteristics are defined between a pair of ports using RSVP,
 defined link stations will need sufficient configured information to
 be matched with incoming XIDs.  (Correct matching of an incoming XID
 to a defined link station allows CS to provide the correct TG
 characteristics to topology and routing services (TRS).)  At that
 time CS will do the mapping based on both the IP address of the
 adjacent node and a predefined TG number.
 The node initiating link activation knows which link it is
 activating.  Some parameters sent in prenegotiation XID are defined
 in the regular link station configuration and not allowed to change
 in following negotiation-proceeding XIDs.  To allow for forward
 migration to RSVP, when a regular TG is activated in an IP network,
 the node receiving the first XID (i.e., the node not initiating link
 activation) must also understand which defined link station is being
 activated before sending a prenegotiation XID in order to correctly
 set parameters that cannot change.  For this reason, the node
 initiating link activation will indicate the TG number in
 prenegotiation XIDs by including a TG Descriptor (X'46') control
 vector containing a TG Identifier (X'80') subfield.  Furthermore, the
 node receiving the first XID will force the node activating the link
 to send the first prenegotiation XID by responding to null XIDs with
 null XIDs.  To prevent potential deadlocks, the node receiving the
 first XID has a limit (the LDLC retry count can be used) on the
 number of null XIDs it will send.  Once this limit is reached, that
 node will send an XID with an XID Negotiation Error (X'22') control
 vector in response to a null XID; sense data X'0809003A' is included
 in the control vector to indicate unexpected null XID.  If the node
 that received the first XID receives a prenegotiation XID without the
 TG Identifier subfield, it will send an XID with an XID Negotiation
 Error control vector to reject the link connection; sense data
 X'088C4680' is included in the control vector to indicate the
 subfield was missing.
 For a regular TG, the TG parameters are provided by the node operator
 based on customer configuration in DEFINE_PORT(RQ) and DEFINE_LS(RQ).
 The following parameters are supplied in DEFINE_LS(RQ) for HPR/IP
 links:

Dudley Informational [Page 14] RFC 2353 APPN/HPR in IP Networks May 1998

 o   The destination IP host name (this parameter can usually be
     mapped to the destination IP address):  If the link is not
     activated at node initialization, the IP host name should be
     mapped to an IP address, and the IP address should be stored with
     the link station definition.  This is required to allow an
     incoming link activation to be matched with the link station
     definition.  If the adjacent node activates the link with a
     different IP address (e.g., it could have multiple ports), it
     will not be possible to match the link activation with the link
     station definition, and the default parameters specified in the
     local port definition will be used.
 o   The destination IP version (set to version 4, support for version
     6 may be required in the future; this parameter is only required
     if the address and version cannot be determined using the
     destination IP host name.)
 o   The destination IP address (in the format specified by the
     destination IP version; this parameter is only required if the
     address cannot be determined using the destination IP host name.)
 o   Source service access point address (SSAP) used for XID, TEST,
     DISC, and DM (default is X'04'; other values may be specified
     when multiple links between a pair of IP addresses are defined)
 o   Destination service access point address (DSAP) used for XID,
     TEST, DISC, and DM (default is X'04')
 o   Source service access point address (SSAP) used for HPR network
     layer packets (NLPs) (default is X'C8'; other values may be
     specified when multiple links between a pair of IP addresses are
     defined.)
 o   Maximum receive BTU size (default is 1461; this parameter is used
     to override the setting in DEFINE_PORT.)
 o   Maximum send BTU size (default is 1461; this parameter is used to
     override the setting in DEFINE_PORT.)
 o   IP precedence (the setting of the 3-bit field within the Type of
     Service byte of the IP header for LLC commands such as XID and
     for each of the APPN transmission priorities; the defaults are
     given in 2.6.1, "IP Prioritization" on page 28; this parameter is
     used to override the settings in DEFINE_PORT)
 o   Shareable with connection network traffic (default is yes for
     non-RSVP links)

Dudley Informational [Page 15] RFC 2353 APPN/HPR in IP Networks May 1998

 o   Retry count for LDLC (default is 3; this parameter is used to
     override the setting in DEFINE_PORT)
 o   Retry timer period for LDLC (default is 15 seconds; a smaller
     value such as 10 seconds can be used for a campus link; this
     parameter is used to override the setting in DEFINE_PORT)
 o   LDLC liveness timer period (default is 10 seconds; this parameter
     is to override the setting in DEFINE_PORT; see 2.3.1, "LDLC ness"
     on page 7)
 o   Auto-activation supported (default is no; may be set to yes when
     the local node has switched access to the IP network)
 o   Limited resource (default is to set in concert with auto-
     activation supported)
 o   Limited resource liveness timer (default is 45 sec.)
 o   Port name
 o   Adjacent CP name (optional)
 o   Local CP-CP sessions supported
 o   Defined TG number (optional)
 o   TG characteristics
 The following figures show the activation and deactivation of regular
 TGs.

Dudley Informational [Page 16] RFC 2353 APPN/HPR in IP Networks May 1998

*——————————————————————*

CS DLC LDLC DMUX UDP

*——————————————————————* . . . . .CONNECT_OUT(RQ) . create . . o—————>o————–>o . . . | new LDLC . . . o—————————–>o . CONNECT_OUT(+RSP)| . . . o←————–* . . . | XID . XID(CMD) . XID *——————————→o—————————–>o—–>

             Figure 3. Regular TG Activation (outgoing)
 In Figure 3 upon receiving START_LS(RQ) from NOF, CS starts the link
 activation process by sending CONNECT_OUT(RQ) to the DLC manager.
 The DLC manager creates an instance of LDLC for the link, informs the
 link demultiplexor, and sends CONNECT_OUT(+RSP) to CS.  Then, CS
 starts the activation XID exchange.

*——————————————————————*

CS DLC LDLC DMUX UDP

*——————————————————————* . . . . . CONNECT_IN(RQ) . XID(CMD) . XID . XID o←————–o←—————————-o←————-o←—- | CONNECT_IN(RSP). create . . *—————>o————–>o . . . | new LDLC . . . o—————————–>o . . | XID(CMD) . . . . *————–>o . . . XID | . . o←——————————* . . | XID . XID(RSP) . XID *——————————→o—————————–>o—–>

             Figure 4. Regular TG Activation (incoming)
 In Figure 4, when an XID is received for a new link, it is passed to
 the DLC manager.  The DLC manager sends CONNECT_IN(RQ) to notify CS
 of the incoming link activation, and CS sends CONNECT_IN(+RSP)
 accepting the link activation.  The DLC manager then creates a new
 instance of LDLC, informs the link demultiplexor, and forwards the
 XID to to CS via LDLC.  CS then responds by sending an XID to the
 adjacent node.

Dudley Informational [Page 17] RFC 2353 APPN/HPR in IP Networks May 1998

 The two following figures show normal TG deactivation (outgoing and
 incoming).

*——————————————————————*

CS DLC LDLC DMUX UDP

*——————————————————————* . . . . . . DEACT . DISC . DISC o——————————→o—————————–>o—–> . DEACT . DM . DM . DM o←——————————o←————o←————-o←—- | DISCONNECT(RQ) . destroy . . . *—————>o————–>o . .

DISCONNECT(RSP) |                              .               .

o←————–* . .

            Figure 5. Regular TG Deactivation (outgoing)
 In Figure 5 upon receiving STOP_LS(RQ) from NOF, CS sends DEACT to
 notify the partner node that the HPR link is being deactivated.  When
 the response is received, CS sends DISCONNECT(RQ) to the DLC manager,
 and the DLC manager deactivates the instance of LDLC.  Upon receiving
 DISCONNECT(RSP), CS sends STOP_LS(RSP) to NOF.

*——————————————————————*

CS DLC LDLC DMUX UDP

*——————————————————————* . . . . . . DEACT . DISC . DISC . DISC o←——————————o←————o←————-o←—- | . | DM . DM | . *—————————–>o—–> | DISCONNECT(RQ) . destroy . . . *—————>o————–>o . . .DISCONNECT(RSP) | . . o←————–* . .

            Figure 6. Regular TG Deactivation (incoming)
 In Figure 6, when an adjacent node deactivates a TG, the local node
 receives a DISC.  CS sends STOP_LS(IND) to NOF.  Because IP is
 connectionless, the DLC manager is not aware that the link has been
 deactivated.  For that reason, CS also needs to send DISCONNECT(RQ)
 to the DLC manager; the DLC manager deactivates the instance of LDLC.

Dudley Informational [Page 18] RFC 2353 APPN/HPR in IP Networks May 1998

2.5.1.1 Limited Resources and Auto-Activation

 To reduce tariff charges, the APPN architecture supports the
 definition of switched links as limited resources.  A limited-
 resource link is deactivated when there are no sessions traversing
 the link.  Intermediate HPR nodes are not aware of sessions between
 logical units (referred to as LU-LU sessions) carried in crossing RTP
 connections; in HPR nodes, limited-resource TGs are deactivated when
 no traffic is detected for some period of time.  Furthermore, APPN
 links may be defined as auto-activatable.  Auto-activatable links are
 activated when a new session has been routed across the link.
 An HPR node may have access to an IP network via a switched access
 link.  In such environments, it may be advisable for customers to
 define regular HPR/IP links as limited resources and as being auto-
 activatable.

2.5.2 IP Connection Networks

 Connection network support for IP networks (option set 2010), is
 described in this section.
 APPN architecture defines single link TGs across the point-to-point
 lines connecting APPN nodes.  The natural extension of this model
 would be to define a TG between each pair of nodes connected to a
 shared access transport facility (SATF) such as a LAN or IP network.
 However, the high cost of the system definition of such a mesh of TGs
 is prohibitive for a network of more than a few nodes.  For that
 reason, the APPN connection network model was devised to reduce the
 system definition required to establish TGs between APPN nodes.
 Other TGs may be defined through the SATF which are not part of the
 connection network.  Such TGs (referred to as regular TGs in this
 document) are required for sessions between control points (referred
 to as CP-CP sessions) but may also be used for LU-LU sessions.
 In the connection network model, a virtual routing node (VRN) is
 defined to represent the SATF.  Each node attached to the SATF
 defines a single TG to the VRN rather than TGs to all other attached
 nodes.
 Topology and routing services (TRS) specifies that a session is to be
 routed between two nodes across a connection network by including the
 connection network TGs between each of those nodes and the VRN in the
 Route Selection control vector (RSCV).  When a network node has a TG
 to a VRN, the network topology information associated with that TG
 includes DLC signaling information required to establish connectivity
 to that node across the SATF.  For an end node, the DLC signaling

Dudley Informational [Page 19] RFC 2353 APPN/HPR in IP Networks May 1998

 information is returned as part of the normal directory services (DS)
 process.  TRS includes the DLC signaling information for TGs across
 connection networks in RSCVs.
 CS creates a dynamic link station when the next hop in the RSCV of an
 ACTIVATE_ROUTE signal received from session services (SS) is a
 connection network TG or when an adjacent node initiates link
 activation upon receiving such an ACTIVATE_ROUTE signal.  Dynamic
 link stations are normally treated as limited resources, which means
 they are deactivated when no sessions are using them.  CP-CP sessions
 are not supported on connections using dynamic link stations because
 CP-CP sessions normally need to be kept up continuously.
 Establishment of a link across a connection network normally requires
 the use of CP-CP sessions to determine the destination IP address.
 Because CP-CP sessions must flow across regular TGs, the definition
 of a connection network does not eliminate the need to define regular
 TGs as well.
 Normally, one connection network is defined on a LAN (i.e., one VRN
 is defined.)  For an environment with several interconnected campus
 IP networks, a single wide-area connection network can be defined; in
 addition, separate connection networks can be defined between the
 nodes connected to each campus IP network.

2.5.2.1 Establishing IP Connection Networks

 Once the port is defined, a connection network can be defined on the
 port.  In order to support multiple TGs from a port to a VRN, the
 connection network is defined by the following process:
 1.  A connection network and its associated VRN are defined on the
     port.  This is accomplished by the node operator issuing a
     DEFINE_CONNECTION_NETWORK(RQ) command to NOF and NOF passing a
     DEFINE_CN(RQ) signal to CS.
 2.  Each TG from the port to the VRN is defined by the node operator
     issuing DEFINE_CONNECTION_NETWORK_TG(RQ) to NOF and NOF passing
     DEFINE_CN_TG(RQ) to CS.
 Prior to implementation of Resource ReSerVation Protocol (RSVP)
 support, only one connection network TG between a port and a VRN is
 required.  In that case, product support for the DEFINE_CN_TG(RQ)
 signal is not required because a single set of port configuration
 parameters for each connection network is sufficient.  If a NOF
 implementation does not support DEFINE_CN_TG(RQ), the parameters
 listed in the following section for DEFINE_CN_TG(RQ), are provided by
 DEFINE_CN(RQ) instead.  Furthermore, the Connection Network TG

Dudley Informational [Page 20] RFC 2353 APPN/HPR in IP Networks May 1998

 Numbers (X'81') subfield in the TG Descriptor (X'46') control vector
 on an activation XID is only required to support multiple connection
 network TGs to a VRN, and its use is optional.
  • —————————————————–*

| NO NOF CS |

  • —————————————————–*

DEFINE_CONNECTION_NETWORK(RQ) DEFINE_CN(RQ) .

        o------------------------>o----------------->o
     DEFINE_CONNECTION_NETWORK(RSP)   DEFINE_CN(RSP) |
        o<------------------------o<-----------------*
   DEFINE_CONNECTION_NETWORK_TG(RQ) DEFINE_CN_TG(RQ) .
        o------------------------>o----------------->o
  DEFINE_CONNECTION_NETWORK_TG(RSP) DEFINE_CN_TG(RSP)|
        o<------------------------o<-----------------*
        Figure 7. IP Connection Network Definition
 An incoming dynamic link activation may be rejected with sense data
 X'10160046' if there is an existing dynamic link between the two
 ports over the same connection network (i.e., with the same VRN CP
 name).  If a node receives an activation XID for a dynamic link with
 an IP address pair, a SAP pair, and a VRN CP name that are the same
 as for an active dynamic link, that node can assume that the link has
 failed and that the partner node is reactivating the link.  In such a
 case as an optimization, the node receiving the XID can take down the
 active link and allow the link to be reestablished in the IP network.
 Because UDP packets can arrive out of order, implementation of this
 optimization requires the use of a timer to prevent a stray XID from
 deactivating an active link.
 Once all the connection networks are defined, the node operator
 issues START_PORT(RQ), NOF passes the associated signal to CS, and CS
 passes ACTIVATE_PORT(RQ) to the DLC manager.  Upon receiving the
 ACTIVATE_PORT(RSP) signal from the DLC manager, CS sends a TG_UPDATE
 signal to TRS for each defined connection network TG.  Each signal
 notifies TRS that a TG to the VRN has been activated and includes TG
 vectors describing the TG.  If the port fails or is deactivated, CS
 sends TG_UPDATE indicating the connection network TGs are no longer
 operational.  Information about TGs between a network node and the
 VRN is maintained in the network topology database.  Information
 about TGs between an end node and the VRN is maintained only in the
 local topology database.  If TRS has no node entry in its topology
 database for the VRN, TRS dynamically creates such an entry.  A VRN
 node entry will become part of the network topology database only if

Dudley Informational [Page 21] RFC 2353 APPN/HPR in IP Networks May 1998

 a network node has defined a TG to the VRN; however, TRS is capable
 of selecting a direct path between two end nodes across a connection
 network without a VRN node entry.

*——————————————————————–*

CS TRS DLC DMUX

*——————————————————————–*

   .            ACTIVATE_PORT(RQ)           .     create
   o--------------------------------------->o----------------->o
   .            ACTIVATE_PORT(RSP)          |                  .
   o<---------------------------------------*                  .
   |  TG_UPDATE         .                   .                  .
   *------------------->o                   .                  .
   .                    .                   .                  .
         Figure 8. IP Connection Network Establishment

The TG vectors for IP connection network TGs include the following information:

 o   TG number
 o   VRN CP name
 o   TG characteristics used during route selection
  1. Effective capacity
  2. Cost per connect time
  3. Cost per byte transmitted
  4. Security
  5. Propagation delay
  6. User defined parameters
 o   Signaling information
  1. IP version (indicates the format of the IP header including

the IP address)

  1. IP address
  1. Link service access point address (LSAP) used for XID, TEST,

DISC, and DM

2.5.2.2 IP Connection Network Parameters

 For a connection network TG, the parameters are determined by CS
 using several inputs.  Parameters that are particular to the local
 port, connection network, or TG are system defined and received in

Dudley Informational [Page 22] RFC 2353 APPN/HPR in IP Networks May 1998

 DEFINE_PORT(RQ), DEFINE_CN(RQ), or DEFINE_CN_TG(RQ).  Signaling
 information for the destination node including its IP address is
 received in the ACTIVATE_ROUTE request from SS.
 The following configuration parameters are received in DEFINE_CN(RQ):
 o   Connection network name (CP name of the VRN)
 o   Limited resource liveness timer (default is 45 sec.)
 o   IP precedence (the setting of the 3-bit field within the Type of
     Service byte of the IP header for LLC commands such as XID and
     for each of the APPN transmission priorities; the defaults are
     given in 2.6.1, "IP Prioritization" on page 28; this parameter is
     used to override the settings in DEFINE_PORT)
 The following configuration parameters are received in
 DEFINE_CN_TG(RQ):
 o   Port name
 o   Connection network name (CP name of the VRN)
 o   Connection network TG number (set to a value between 1 and 239)
 o   TG characteristics (see 2.6.3, "Default TG Characteristics" on
     page 30)
 o   Link service access point address (LSAP) used for XID, TEST,
     DISC, and DM (default is X'04')
 o   Link service access point address (LSAP) used for HPR network
     layer packets (default is X'C8')
 o   Limited resource (default is yes)
 o   Retry count for LDLC (default is 3; this parameter is used to
     override the setting in DEFINE_PORT)
 o   Retry timer period for LDLC (default is 15 sec.; a smaller value
     such as 10 seconds can be used for a campus connection network;
     this parameter is used to override the setting in DEFINE_PORT)
 o   LDLC liveness timer period (default is 10 seconds; this parameter
     is used to override the setting in DEFINE_PORT; see 2.3.1, "LDLC
     Liveness" on page 7)

Dudley Informational [Page 23] RFC 2353 APPN/HPR in IP Networks May 1998

 o   Shareable with other HPR traffic (default is yes for non-RSVP
     links)
 o   Maximum receive BTU size (default is 1461; this parameter is used
     to override the value in DEFINE_PORT(RQ).)
 o   Maximum send BTU size (default is 1461; this parameter is used to
     override the value in DEFINE_PORT(RQ).)
 The following parameters are received in ACTIVATE_ROUTE for
 connection network TGs:
 o   The TG pair
 o   The destination IP version (if this version is not supported by
     the local node, the ACTIVATE_ROUTE_RSP reports the activation
     failure with sense data X'086B46A5'.)
 o   The destination IP address (in the format specified by the
     destination IP version)
 o   Destination service access point address (DSAP) used for XID,
     TEST, DISC, and DM

2.5.2.3 Sharing of TGs

 Connection network traffic is multiplexed onto a regular defined IP
 TG (usually used for CP-CP session traffic) in order to reduce the
 control block storage.  No XIDs flow to establish a new TG on the IP
 network, and no new LLC is created.  When a regular TG is shared,
 incoming traffic is demultiplexed using the normal means.  If the
 regular TG is deactivated, a path switch is required for the HPR
 connection network traffic sharing the TG.
 Multiplexing is possible if the following conditions hold:
 1.  Both the regular TG and the connection network TG to the VRN are
     defined as shareable between HPR traffic streams.
 2.  The destination IP address is the same.
 3.  The regular TG is established first.  (Because links established
     for connection network traffic do not support CP-CP sessions,
     there is little value in allowing a regular TG to share such a
     link.)
 The destination node is notified via XID when a TG can be shared
 between HPR data streams.  At either end, upon receiving

Dudley Informational [Page 24] RFC 2353 APPN/HPR in IP Networks May 1998

 ACTIVATE_ROUTE requesting a shared TG for connection network traffic,
 CS checks its TGs for one meeting the required specifications before
 initiating a new link.  First, CS looks for a link established for
 the TG pair; if there is no such link, CS determines if there is a
 regular TG that can be shared and, if multiple such TGs exist, which
 TG to choose.  As a result, RTP connections routed over the same TG
 pair may actually use different links, and RTP connections routed
 over different TG pairs may use the same link.

2.5.2.4 Minimizing RSCV Length

 The maximum length of a Route Selection (X'2B') control vector (RSCV)
 is 255 bytes.  Use of connection networks significantly increases the
 size of the RSCV contents required to describe a "hop" across an
 SATF.  First, because two connection network TGs are used to specify
 an SATF hop, two TG Descriptor (X'46') control vectors are required.
 Furthermore, inclusion of DLC signaling information within the TG
 Descriptor control vectors increases the length of these control
 vectors.  As a result, the total number of hops that can be specified
 in RSCVs traversing connection networks is reduced.
 To avoid unnecessarily limiting the number of hops, a primary goal in
 designing the formats for IP signaling information is to minimize
 their size.  Additional techniques are also used to reduce the effect
 of the RSCV length limitation.
 For an IP connection network, DLC signaling information is required
 only for the second TG (i.e., from the VRN to the destination node);
 the signaling information for the first TG is locally defined at the
 origin node.  For this reason, the topology database does not include
 DLC signaling information for the entry describing a connection
 network TG from a network node to a VRN.  The DLC signaling
 information is included in the allied entry for the TG in the
 opposite direction.  This mechanism cannot be used for a connection
 network TG between a VRN and an end node.  However, a node
 implementing IP connection networks does not include IP signaling
 information for the first connection network TG when constructing an
 RSCV.
 In an environment where APPN network nodes are used to route between
 legacy LANs and wide-area IP networks, it is recommended that
 customers not define connection network TGs between these network
 nodes and VRNs representing legacy LANs.  Typically, defined links
 are required between end nodes on the legacy LANs and such network
 nodes which also act as network node servers for the end nodes.
 These defined links can be used for user traffic as well as control
 traffic.  This technique will reduce the number of connection network
 hops in RSCVs between end nodes on different legacy LANs.

Dudley Informational [Page 25] RFC 2353 APPN/HPR in IP Networks May 1998

 Lastly, for environments where RSCVs are still not able to include
 enough hops, extended border nodes (EBNs) can be used to partition
 the network.  In this case, the EBNs will also provide piecewise
 subnet route calculation and RSCV swapping.  Thus, the entire route
 does not need to be described in a single RSCV with its length
 limitation.

2.5.3 XID Changes

 Packets transmitted over IP networks are lost or arrive out of order
 more often than packets transmitted over other "link" technologies.
 As a result, the following problem with the XID3 negotiation protocol
 was exposed:
  1. ——————————————————————-
  • ———————————*

|Node A Node B|

  • ———————————*

o

                        o
                        o
                         XID3 (np, NEG)
           o<-------------------------o
           |XID3 (np, SEC)
           *------------------------->o
                        XID3 (np, PRI)|
                      lost<-----------*
         time out
            XID3 (np, SEC)
           o------------------------->o
                             SETMODE  |
           o<-------------------------*
  fail because never
  received XID3 (np, PRI)
 Notation: np  - negotiation proceeding
           NEG - negotiable link station role
           SEC - secondary link station role
           PRI - primary link station role
  1. ——————————————————————-

Figure 9. XID3 Protocol Problem

 In the above sequence, the XID3(np, PRI), which is a link-level
 response to the received XID3(np, SEC), is lost.  Node A times out
 and resends the XID3(np, SEC) as a link-level command.  When Node B

Dudley Informational [Page 26] RFC 2353 APPN/HPR in IP Networks May 1998

 receives this command, it thinks that the XID3(np, PRI) was
 successfully received by Node A and that the activation XID exchange
 is complete.  As a result, Node B sends SETMODE (SNRM, SABME, or
 XID_DONE_RQ, depending upon the link type).  When Node A receives
 SETMODE, it fails the link activation because it has not received an
 XID3(np, PRI) from Node B confirming that Node B does indeed agree to
 be the primary.  Moreover, there are similar problems with incomplete
 TG number negotiation.
 To solve the problems with incomplete role and TG number negotiation,
 two new indicators are defined in XID3.  The problems are solved only
 if both link stations support these new indicators:
 o   Negotiation Complete Supported indicator (byte 12 bit 0) -- this
     1-bit field indicates whether the Negotiation Complete indicator
     is supported.  This field is meaningful when the XID exchange
     state is negotiation proceeding; otherwise, it is reserved.  A
     value of 0 means the Negotiation Complete indicator is not
     supported; a value of 1 means the indicator is supported.
 o   Negotiation Complete indicator (byte 12 bit 1) -- this 1-bit
     field is meaningful only when the XID exchange state is
     negotiation proceeding, the XID3 is sent by the secondary link
     station, and the Negotiation Complete Supported indicator is set
     to 1; otherwise, this field is reserved.  This field is set to 1
     by a secondary link station that supports enhanced XID
     negotiation when it considers the activation XID negotiation to
     be complete for both link station role and TG number (i.e., it is
     ready to receive a SETMODE command from the primary link
     station.)
 When a primary link station that supports enhanced XID negotiation
 receives an XID3(np) with both the Negotiation Complete Supported
 indicator and the Negotiation Complete indicator set to 1, the
 primary link station will know that it can safely send SETMODE if it
 also considers the XID negotiation to be complete.  The new
 indicators are used as shown in the following sequence when both the
 primary and secondary link stations support enhanced XID negotiation.

Dudley Informational [Page 27] RFC 2353 APPN/HPR in IP Networks May 1998

  1. ——————————————————————-
  • ———————————-*

|Node A Node B |

  • ———————————-*

o

                        o
                        o
                  XID3 (np, NEG, S, ^C)
 1         o<--------------------------o
           |XID3 (np, SEC, S, ^C)
 2         *-------------------------->o
                  XID3 (np, PRI, S, ^C)|
 3                    lost <-----------*
         time out
            XID3 (np, SEC, S, ^C)
 4         o-------------------------->o
                  XID3 (np, PRI, S, ^C)|
 5         o<--------------------------*
           |XID3 (np, SEC, S, C)
 6         *-------------------------->o
                              SETMODE  |
 7         o<--------------------------*
 ^S indicates that byte 12 bit 0 is set to 0.
  S indicates that byte 12 bit 0 is set to 1.
 ^C indicates that byte 12 bit 1 is set to 0.
  C indicates that byte 12 bit 1 is set to 1.
  1. ——————————————————————-

Figure 10. Enhanced XID Negotiation

 When Node B receives the XID in flow 4, it realizes that the Node A
 does not consider XID negotiation to be complete; as a result, it
 resends its current XID information in flow 5.  When Node A receives
 this XID, it responds in flow 6 with an XID that indicates XID
 negotiation is complete.  At this point, Node B, acting as the
 primary link station, sends SETMODE, and the link is activated
 successfully.
 Migration cases with only one link station supporting enhanced XID
 negotiation are shown in the two following sequences.  In the next
 sequence, only Node A (acting as the secondary link station) supports
 the new function.

Dudley Informational [Page 28] RFC 2353 APPN/HPR in IP Networks May 1998

  1. ——————————————————————-
  • ———————————*

|Node A Node B|

  • ———————————*

o

                        o
                        o
                     XID3 (np, NEG, ^S)
 1         o<--------------------------o
           |XID3 (np, SEC, S, ^C)
 2         *-------------------------->o
                     XID3 (np, PRI, ^S)|
 3                    lost <-----------*
         time out
            XID3 (np, SEC, S, ^C)
 4         o-------------------------->o
                              SETMODE  |
 5         o<--------------------------*
         fail
  1. ——————————————————————-

Figure 11. First Migration Case

 The XID negotiation fails because Node B does not understand the new
 indicators and responds to flow 4 with SETMODE.
 In the next sequence, Node B supports the new indicators but Node A
 does not.

Dudley Informational [Page 29] RFC 2353 APPN/HPR in IP Networks May 1998

  1. ——————————————————————-
  • ———————————*

|Node A Node B|

  • ———————————*

o

                        o
                        o
                  XID3 (np, NEG, S, ^C)
 1         o<--------------------------o
           |XID3 (np, SEC, ^S)
 2         *-------------------------->o
                  XID3 (np, PRI, S, ^C)|
 3                    lost <-----------*
         time out
            XID3 (np, SEC, ^S)
 4         o-------------------------->o
                               SETMODE |
 5         o<--------------------------*
         fail
  1. ———————————————————————–

Figure 12. Second Migration Case

 The XID negotiation fails because Nobe A does not understand the new
 indicators and thus cannot indicate that it thinks XID negotiation is
 not complete in flow 4.  Node B understands that the secondary link
 station (node A) does not support the new indicators and respond with
 SETMODE in flow 5.
 Products that support HPR/IP links are required to support enhanced
 XID negotiation.  Moreover, it is recommended that products
 implementing this solution for HPR/IP links also support it for other
 link types.

2.5.4 Unsuccessful IP Link Activation

 Link activation may fail for several different reasons.  When link
 activation over a connection network or of an auto-activatable link
 is attempted upon receiving ACTIVATE_ROUTE from SS, activation
 failure is reported with ACTIVATE_ROUTE_RSP containing sense data
 explaining the cause of failure.  Likewise, when activation fails for
 other regular defined links, the failure is reported with
 START_LS(RSP) containing sense data.

Dudley Informational [Page 30] RFC 2353 APPN/HPR in IP Networks May 1998

 As is normal for session activation failures, the sense data is also
 sent to the node that initiated the session.  At the APPN-to-HPR
 boundary, a -RSP(BIND) or an UNBIND with an Extended Sense Data
 control vector is generated and returned to the primary logical unit
 (PLU).
 At an intermediate HPR node, link activation failure can be reported
 with sense data X'08010000' or X'80020000'.  At a node with route-
 selection responsibility, such failure can be reported with sense
 data X'80140001'.
 The following table contains the sense data for the various causes of
 link activation failure:

Dudley Informational [Page 31] RFC 2353 APPN/HPR in IP Networks May 1998

+———————————————————————-+

Table 1 (Page 1 of 2). Native IP DLC Link Activation Failure Sense
Data

+——————————————————–+————-+

ERROR DESCRIPTION SENSE DATA

+——————————————————–+————-+

The link specified in the RSCV is not available. X'08010000'

+——————————————————–+————-+

The limit for null XID responses by a called node was X'0809003A'
reached.

+——————————————————–+————-+

A BIND was received over a subarea link, but the next X'08400002'
hop is over a port that supports only HPR links. The
receiver does not support this configuration.

+——————————————————–+————-+

The contents of the DLC Signaling Type (X'91') X'086B4691'
subfield of the TG Descriptor (X'46') control vector
contained in the RSCV were invalid.

+——————————————————–+————-+

The contents of the IP Address and Link Service Access X'086B46A5'
Point Address (X'A5') subfield of the TG Descriptor
(X'46') control vector contained in the RSCV were
invalid.

+——————————————————–+————-+

No DLC Signaling Type (X'91') subfield was found in X'086D4691'
the TG Descriptor (X'46') control vector contained in
the RSCV.

+——————————————————–+————-+

No IP Address and Link Service Access Point Address X'086D46A5'
(X'A5') subfield was found in the TG Descriptor
(X'46') control vector contained in the RSCV.

+——————————————————–+————-+

Multiple sets of DLC signaling information were found X'08770019'
in the TG Descriptor (X'46') control vector contained
in the RSCV. IP supports only one set of DLC
signaling information.

+——————————————————–+————-+

Link Definition Error: A link is defined as not X'08770026'
supporting HPR, but the port only supports HPR links.

+——————————————————–+————-+

A called node found no TG Identifier (X'80') subfield X'088C4680'
within a TG Descriptor (X'46') control vector in a
prenegotiation XID for a defined link in an IP
network.

+——————————————————–+————-+

Dudley Informational [Page 32] RFC 2353 APPN/HPR in IP Networks May 1998

+———————————————————————-+

Table 1 (Page 2 of 2). Native IP DLC Link Activation Failure Sense
Data

+——————————————————–+————-+

The XID3 received from the adjacent node does not X'10160031'
contain an HPR Capabilities (X'61') control vector.
The IP port supports only HPR links.

+——————————————————–+————-+

The RTP Supported indicator is set to 0 in the HPR X'10160032'
Capabilities (X'61') control vector of the XID3
received from the adjacent node. The IP port supports
only links to nodes that support RTP.

+——————————————————–+————-+

The Control Flows over RTP Supported indicator is set X'10160033'
to 0 in the HPR Capabilities (X'61') control vector of
the XID3 received from the adjacent node. The IP port
supports only links to nodes that support control
flows over RTP.

+——————————————————–+————-+

The LDLC Supported indicator is set to 0 in the HPR X'10160034'
Capabilities (X'61') control vector of the XID3
received from the adjacent node. The IP port supports
only links to nodes that support LDLC.

+——————————————————–+————-+

The HPR Capabilities (X'61') control vector received X'10160044'
in XID3 does not include an IEEE 802.2 LLC (X'80') HPR
Capabilities subfield. The subfield is required on an
IP link.

+——————————————————–+————-+

Multiple defined links between a pair of switched X'10160045'
ports is not supported by the local node. A link
activation request was received for a defined link,
but there is an active defined link between the paired
switched ports.

+——————————————————–+————-+

Multiple dynamic links across a connection network X'10160046'
between a pair of switched ports is not supported by
the local node. A link activation request was
received for a dynamic link, but there is an active
dynamic link between the paired switched ports across
the same connection network.

+——————————————————–+————-+

Link failure X'80020000'

+——————————————————–+————-+

Route selection services has determined that no path X'80140001'
to the destination node exists for the specified COS.

+——————————————————–+————-+

Dudley Informational [Page 33] RFC 2353 APPN/HPR in IP Networks May 1998

2.6 IP Throughput Characteristics

2.6.1 IP Prioritization

 Typically, IP routers process packets on a first-come-first-served
 basis; i.e., no packets are given transmission priority.  However,
 some IP routers prioritize packets based on IP precedence (the 3-bit
 field within the Type of Service byte of the IP header) or UDP port
 numbers.  (With the current plans for IP security, the UDP port
 numbers are encrypted; as a result, IP routers would not be able to
 prioritize encrypted traffic based on the UDP port numbers.)  HPR
 will be able to exploit routers that provide priority function.
 The 5 UDP port numbers, 12000-12004 (decimal), have been assigned by
 the Internet Assigned Number Authority (IANA).  Four of these port
 numbers are used for ANR-routed network layer packets (NLPs) and
 correspond to the APPN transmission priorities (network, 12001; high,
 12002; medium, 12003; and low, 12004), and one port number (12000) is
 used for a set of LLC commands (i.e., XID, TEST, DISC, and DM) and
 function-routed NLPs (i.e., XID_DONE_RQ and XID_DONE_RSP).  These
 port numbers are used for "listening" and are also used in the
 destination port number field of the UDP header of transmitted
 packets.  The source port number field of the UDP header can be set
 either to one of these port numbers or to an ephemeral port number.
 The IP precedence for each transmission priority and for the set of
 LLC commands (including function-routed NLPs) are configurable.  The
 implicit assumption is that the precedence value is associated with
 priority queueing and not with bandwidth allocation; however,
 bandwidth allocation policies can be administered by matching on the
 precedence field.  The default mapping to IP precedence is shown in
 the following table:

Dudley Informational [Page 34] RFC 2353 APPN/HPR in IP Networks May 1998

 +---------------------------------------------+
 | Table 2. Default IP Precedence Settings     |
 +----------------------+----------------------+
 | PRIORITY             |      PRECEDENCE      |
 +----------------------+----------------------+
 | LLC commands and     |          110         |
 | function-routed NLPs |                      |
 +----------------------+----------------------+
 | Network              |          110         |
 +----------------------+----------------------+
 | High                 |          100         |
 +----------------------+----------------------+
 | Medium               |          010         |
 +----------------------+----------------------+
 | Low                  |          001         |
 +----------------------+----------------------+
 As an example, with this default mapping, telnet, interactive ftp,
 and business-use web traffic could be mapped to a precedence value of
 011, and batch ftp could be mapped to a value of 000.
 These settings were devised based on the AIW's understanding of the
 intended use of IP precedence.  The use of IP precedence will be
 modified appropriately if the IETF standardizes its use differently.
 The other fields in the IP TOS byte are not used and should be set to
 0.
 For outgoing ANR-routed NLPs, the destination (and optionally the
 source) UDP port numbers and IP precedence are set based on the
 transmission priority specified in the HPR network header.
 It is expected that the native IP DLC architecture described in this
 document will be used primarily for private campus or wide-area
 intranets where the customer will be able to configure the routers to
 honor the transmission priority associated with the UDP port numbers
 or IP precedence.  The architecture can be used to route HPR traffic
 in the Internet; however, in that environment, routers do not
 currently provide the priority function, and customers may find the
 performance unacceptable.
 In the future, a form of bandwidth reservation may be possible in IP
 networks using the Resource ReSerVation Protocol (RSVP), or the
 differentiated services currently being studied by the Integrated
 Services working group of the IETF.  Bandwidth could be reserved for
 an HPR/IP link thus insulating the HPR traffic from congestion
 associated with the traffic of other protocols.

Dudley Informational [Page 35] RFC 2353 APPN/HPR in IP Networks May 1998

2.6.2 APPN Transmission Priority and COS

 APPN transmission priority and class of service (COS) allow APPN TGs
 to be highly utilized with batch traffic without impacting the
 performance of response-time sensitive interactive traffic.
 Furthermore, scheduling algorithms guarantee that lower-priority
 traffic is not completely blocked.  The result is predictable
 performance.
 When a session is initiated across an APPN network, the session's
 mode is mapped into a COS and transmission priority.  For each COS,
 APPN has a COS table that is used in the route selection process to
 select the most appropriate TGs (based on their TG characteristics)
 for the session to traverse.  The TG characteristics and COS tables
 are defined such that APPN topology and routing services (TRS) will
 select the appropriate TG for the traffic of each COS.

2.6.3 Default TG Characteristics

 In Chapter 7 (TRS) of [1], there is a set of SNA-defined TG default
 profiles.  When a TG (connection network or regular) is defined as
 being of a particular technology (e.g., ethernet or X.25) without
 specification of the TG's characteristics, parameters from the
 technology's default profile are used in the TG's topology entry.
 The customer is free to override these values via configuration.
 Some technologies have multiple profiles (e.g., ISDN has both a
 profile for switched and nonswitched.)  Two default profiles are
 required for IP TGs.  This many are needed because there are both
 campus and wide-area IP networks.  As a result for each HPR/IP TG, a
 customer should specify, at minimum, campus or wide area.  HPR/IP TGs
 traversing the Internet should be specified as wide-area links.  If
 no specification is made, a campus network is assumed.
 The 2 IP profiles are as follows:

+———————————————————————-+

Table 3. IP Default TG Characteristics

+——————-+———+———-+———+———+———+

Cost Cost per Security Propa- Effec-
per byte gation tive
connect delay capacity
time

+——————-+———+———-+———+———+———+

Campus 0 0 X'01' X'71' X'75'

+——————-+———+———-+———+———+———+

Wide area 0 0 X'20' X'91' X'43'

+——————-+———+———-+———+———+———+

Dudley Informational [Page 36] RFC 2353 APPN/HPR in IP Networks May 1998

 Typically, a TG is either considered to be "free" if it is owned or
 leased or "costly" if it is a switched carrier facility.  Free TGs
 have 0 for both cost parameters, and costly TGs have 128 for both
 parameters.  For campus IP networks, the default for both cost
 parameters is 0.
 It is less clear what the defaults should be for wide area.  Because
 a router normally has leased access to an IP network, the defaults
 for both costs are also 0.  This assumes the IP network is not
 tariffed.  However, if the IP network is tariffed, then the customer
 should set the cost per byte to 0 or 128 depending on whether the
 tariff contains a component based on quantity of data transmitted,
 and the customer should set the cost per connect time to 0 or 128
 based on whether there is a tariff component based on connect time.
 Furthermore, for switched access to the IP network, the customer
 settings for both costs should also reflect the tariff associated
 with the switched access link.
 Only architected values (see "Security" in [1]) may be used for a
 TG's security parameter.  The default security value is X'01'
 (lowest) for campus and X'20' (public switched network; secure in the
 sense that there is no predetermined route the traffic will take) for
 wide-area IP networks.  The network administrator may override the
 default value but should, in that case, ensure that an appropriate
 level of security exists.
 For wide area, the value X'91' (packet switched) is the default for
 propagation delay; this is consistent with other wide-area facilities
 and indicates that IP packets will experience both terrestrial
 propagation delay and queueing delay in intermediate routers.  This
 value is suitable for both the Internet and wide-area intranets;
 however, the customer could use different values to favor intranets
 over the Internet during route selection.  The value X'99' (long) may
 be appropriate for some international links across the Internet.  For
 campus, the default is X'71' (terrestrial); this setting essentially
 equates the queueing delay in IP networks with terrestrial
 propagation delay.
 For wide area, X'43' (56 kbs) is shown as the default effective
 capacity; this is at the low-end of typical speeds for wide-area IP
 links.  For campus, X'75' (4 Mbs) is the default; this is at the
 low-end of typical speeds for campus IP links.  However, customers
 should set the effective capacity for both campus and wide area IP
 links based on the actual physical speed of the access link to the IP
 network; for regular links, if both the source and destination access
 speeds are known, customers should set the effective capacity based
 on the minimum of these two link speeds.  If there are multiple
 access links, the capacity setting should be based on the physical

Dudley Informational [Page 37] RFC 2353 APPN/HPR in IP Networks May 1998

 speed of the access link that is expected to be used for the link.
 For the encoding technique for effective capacity in the topology
 database, see "Effective Capacity" in Chapter 7, Topology and Routing
 Services of [1].  The table in that section can be extended as
 follows for higher speeds:

+———————————————————————-+

Table 4. Calculated Effective Capacity Representations

+———————————–+———————————-+

Link Speed (Approx.) Effective Capacity

+———————————–+———————————-+

25M X'8A'

+———————————–+———————————-+

45M X'91'

+———————————–+———————————-+

100M X'9A'

+———————————–+———————————-+

155M X'A0'

+———————————–+———————————-+

467M X'AC'

+———————————–+———————————-+

622M X'B0'

+———————————–+———————————-+

1G X'B5'

+———————————–+———————————-+

1.9G X'BC'

+———————————–+———————————-+

2.6.4 SNA-Defined COS Tables

 SNA-defined batch and interactive COS tables are provided in [1].
 These tables are enhanced in [2] (see section 18.7.2) for the
 following reasons:
 o   To ensure that the tables assign reasonable weights to ATM TGs
     relative to each other and other technologies based on cost,
     speed, and delay
 o   To facilitate use of other new higher-speed facilities - This
     goal is met by providing several speed groupings above 10 Mbps.
     To keep the tables from growing beyond 12 rows, low-speed
     groupings are merged.
 Products implementing the native IP DLC should use the new COS
 tables.  Although the effective capacity values in the old tables are
 sufficient for typical IP speeds, the new tables are valuable because
 higher-speed links can be used for IP networks.

Dudley Informational [Page 38] RFC 2353 APPN/HPR in IP Networks May 1998

2.6.5 Route Setup over HPR/IP links

 The Resequence ("REFIFO") indicator is set in Route Setup request and
 reply when the RTP path uses a multi-link TG because packets may not
 be received in the order sent.  The Resequence indicator is also set
 when the RTP path includes an HPR/IP link as packets sent over an IP
 network may arrive out of order.
 Adaptive rate-based congestion control (ARB) is an HPR Rapid
 Transport Protocol (RTP) function that controls the data transmission
 rate over RTP connections.  ARB also provides fairness between the
 RTP traffic streams sharing a link.  For ARB to perform these
 functions in the IP environment, it is necessary to coordinate the
 ARB parameters with the IP TG characteristics.  This is done for IP
 links in a similar manner to that done for other link types.

2.6.6 Access Link Queueing

 Typically, nodes implementing the native IP DLC have an access link
 to a network of IP routers.  These IP routers may be providing
 prioritization based on UDP port numbers or IP precedence.  A node
 implementing the native IP DLC can be either an IP host or an IP
 router; in both cases, such nodes should also honor the priorities
 associated with either the UDP port numbers or the IP precedence when
 transmitting HPR data over the access link to the IP network.

*——–* access link *——–* *——–*

HPR ————- IP —– IP
node Router Router

*——–* *——–* *——–*

                          |              |
                          |              |
                          |              |
                     *--------*     *--------* access link *--------*
                     |   IP   |-----|   IP   |-------------|  HPR   |
                     | Router |     | Router |             |  node  |
                     *--------*     *--------*             *--------*

                      Figure 13. Access Links
 Otherwise, the priority function in the router network will be
 negated with the result being HPR interactive traffic delayed by
 either HPR batch traffic or the traffic of other higher-layer
 protocols at the access link queues.

Dudley Informational [Page 39] RFC 2353 APPN/HPR in IP Networks May 1998

2.7 Port Link Activation Limits

 Three parameters are provided by NOF to CS on DEFINE_PORT(RQ) to
 define the link activation limits for a port: total limit, inbound
 limit, and outbound limit.  The total limit is the desired maximum
 number of active link stations allowed on the port for both regular
 TGs and connection network TGs.  The inbound limit is the desired
 number of link stations reserved for connections initiated by
 adjacent nodes; the purpose of this field is to insure that a minimum
 number of link stations may be activated by adjacent nodes.  The
 outbound limit is the desired number of link stations reserved for
 connections initiated by the local node.  The sum of the inbound and
 outbound limits must be less than or equal to the total limit.  If
 the sum is less than the total limit, the difference is the number of
 link stations that can be activated on a demand basis as either
 inbound or outbound.  These limits should be based on the actual
 adapter capability and the node's resources (e.g., control blocks).
 A connection network TG will be reported to topology as quiescing
 when its port's total limit threshold is reached; likewise, an
 inactive auto-activatable regular TG is reported as nonoperational.
 When the number of active link stations drops far enough below the
 threshold (e.g., so that at least 20 percent of the original link
 activation limit has been recovered), connection network TGs are
 reported as not quiescing, and auto-activatable TGs are reported as
 operational.

2.8 Network Management

 APPN and HPR management information is defined by the APPN MIB (RFC
 2155 [11]) and the HPR MIB (RFC 2238 [13]).  In addition, the SNANAU
 working group of the IETF plans to define an HPR-IP-MIB that will
 provide HPR/IP-specific management information.  In particular, this
 MIB will provide a mapping of APPN traffic types to IP Type of
 Service Precedence values, as well as a count of UDP packets sent for
 each traffic type.
 There are also rules that must be specified concerning the values an
 HPR/IP implementation returns for objects in the APPN MIB:
 o   Several objects in the APPN MIB have the syntax IANAifType.  The
     value 126, defined as "IP (for APPN HPR in IP networks)" should
     be returned by the following three objects when they identify an
     HPR/IP link:
  1. appnPortDlcType
  2. appnLsDlcType
  3. appnLsStatusDlcType

Dudley Informational [Page 40] RFC 2353 APPN/HPR in IP Networks May 1998

 o   Link-level addresses are reported in the following objects:
  1. appnPortDlcLocalAddr
  2. appnLsLocalAddr
  3. appnLsRemoteAddr
  4. appnLsStatusLocalAddr
  5. appnLsStatusRemoteAddr
     All of these objects should return ASCII character strings that
     represent IP addresses in the usual dotted-decimal format.  (At
     this point it's not clear what the "usual...format" will be for
     IPv6 addresses, but whatever it turns out to be, that is what
     these objects will return when an HPR/IP link traverses an IP
     network.)
 o   The following two objects return Object Identifiers that tie
     table entries in the APPN MIB to entries in lower-layer MIBs:
  1. appnPortSpecific
  2. appnLsSpecific
     Both of these objects should return the same value:  a RowPointer
     to the ifEntry in the agent's ifTable for the physical interface
     associated with the local IP address for the port.  If the agent
     implements the IP-MIB (RFC 2011 [12]), this association between
     the IP address and the physical interface will be represented in
     the ipNetToMediaTable.

2.9 IPv4-to-IPv6 Migration

 The native IP DLC is architected to use IP version 4 (IPv4).
 However, support for IP version 6 (IPv6) may be required in the
 future.
 IP routers and hosts can interoperate only if both ends use the same
 version of the IP protocol.  However, most IPv6 implementations
 (routers and hosts) will actually have dual IPv4/IPv6 stacks.  IPv4
 and IPv6 traffic can share transmission facilities provided that the
 router/host at each end has a dual stack.  IPv4 and IPv6 traffic will
 coexist on the same infrastructure in most areas.  The version number
 in the IP header is used to map incoming packets to either the IPv4
 or IPv6 stack.  A dual-stack host which wishes to talk to an IPv4
 host will use IPv4.
 Hosts which have an IPv4 address can use it as an IPv6 address using
 a special IPv6 address prefix (i.e., it is an embedded IPv4 address).
 This mapping was provided mainly for "legacy" application
 compatibility purposes as such applications don't have the socket

Dudley Informational [Page 41] RFC 2353 APPN/HPR in IP Networks May 1998

 structures needed to store full IPv6 addresses.  Two IPv6 hosts may
 communicate using IPv6 with embedded-IPv4 addresses.
 Both IPv4 and IPv6 addresses can be stored by the domain name service
 (DNS). When an application queries DNS, it asks for IPv4 addresses,
 IPv6 addresses, or both. So, it's the application that decides which
 stack to use based on which addresses it asks for.
 Migration for HPR/IP ports will work as follows:
 An HPR/IP port is configured to support IPv4, IPv6, or both.  If IPv4
 is supported, a local IPv4 address is defined; if IPv6 is supported,
 a local IPv6 address (which can be an embedded IPv4 address) is
 defined.  If both IPv4 and IPv6 are supported, both a local IPv4
 address and a local IPv6 address are defined.
 Defined links will work as follows:  If the local node supports IPv4
 only, a destination IPv4 address may be defined, or an IP host name
 may be defined in which case DNS will be queried for an IPv4 address.
 If the local node supports IPv6 only, a destination IPv6 address may
 be defined, or an IP host name may be defined in which case DNS will
 be queried for an IPv6 address.  If both IPv4 and IPv6 are supported,
 a destination IPv4 address may be defined, a destination IPv6 address
 may be defined, or an IP host name may be defined in which case DNS
 will be queried for both IPv4 and IPv6 addresses; if provided by DNS,
 an IPv6 address can be used, and an IPv4 address can be used
 otherwise.
 Separate IPv4 and IPv6 connection networks can be defined.  If the
 local node supports IPv4, it can define a connection network TG to
 the IPv4 VRN.  If the local node supports IPv6, it can define a TG to
 the IPv6 VRN.  If both are supported, TGs can be defined to both
 VRNs.  Therefore, the signaling information received in RSCVs will be
 compatible with the local node's capabilities unless a configuration
 error has occurred.

3.0 References

 [1]  IBM, Systems Network Architecture Advanced Peer-to-Peer
 Networking Architecture Reference, SC30-3442-04. Viewable at URL:
 http://www.raleigh.ibm.com/cgi-bin/bookmgr/BOOKS/D50L0000/CCONTENTS
 [2]  IBM, Systems Network Architecture Advanced Peer-to-Peer
 Networking High Performance Routing Architecture Reference, Version
 3.0, SV40-1018-02.  Viewable at URL: http://www.raleigh.ibm.com/cgi-
 bin/bookmgr/BOOKS/D50H6001/CCONTENTS

Dudley Informational [Page 42] RFC 2353 APPN/HPR in IP Networks May 1998

 [3]  IBM, Systems Network Architecture Formats, GA27-3136-16.
 Viewable at URL: http://www.raleigh.ibm.com/cgi-
 bin/bookmgr/BOOKS/D50A5003/CCONTENTS
 [4]  Wells, L. and A. Bartky, "Data Link Switching: Switch-to-Switch
 Protocol, AIW DLSw RIG:  DLSw Closed Pages, DLSw Standard Version
 1.0", RFC 1795, April 1995.
 [5]  Bryant, D. and P. Brittain, "APPN Implementers' Workshop Closed
 Pages Document DLSw v2.0 Enhancements", RFC 2166, June 1997.
 [6]  Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
 1980.
 [7]  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.
 [8]  Almquist, P., "Type of Service in the Internet Protocol Suite",
 RFC 1349, July 1992.
 [9]  Braden, R., "Requirements for Internet Hosts -- Communication
 Layers", STD 3, RFC 1122, October 1989.
 [10] Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin,
 "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
 Specification", RFC 2205, September 1997.
 [11] Clouston, B., and B. Moore, "Definitions of Managed Objects for
 APPN using SMIv2", RFC 2155, June 1997.
 [12] McCloghrie, K., "SNMPv2 Management Information Base for the
 Internet Protocol using SMIv2", RFC 2011, November 1996.
 [13] Clouston, B., and B. Moore, "Definitions of Managed Objects for
 HPR using SMIv2", RFC 2238, November 1997.

4.0 Security Considerations

 For HPR, the IP network appears to be a link.  For that reason, the
 SNA session-level security functions (user authentication, LU
 authentication, session encryption, etc.) are still available for
 use.  In addition, as HPR traffic flows as UDP datagrams through the
 IP network, IPsec can be used to provide network-layer security
 inside the IP network.
 There are firewall considerations when supporting HPR traffic using
 the native IP DLC.  First, the firewall filters can be set to allow
 the HPR traffic to pass.  Traffic can be restricted based on the
 source and destination IP addresses and the destination port number;

Dudley Informational [Page 43] RFC 2353 APPN/HPR in IP Networks May 1998

 the source port number is not relevant.  That is, the firewall should
 accept traffic with the IP addresses of the HPR/IP nodes and with
 destination port numbers in the range 12000 to 12004.  Second, the
 possibility exists for an attack using forged UDP datagrams; such
 attacks could cause the RTP connection to fail or even introduce
 false data on a session.  In environments where such attacks are
 expected, the use of network-layer security is recommended.

5.0 Author's Address

 Gary Dudley
 C3BA/501
 IBM Corporation
 P.O. Box 12195
 Research Triangle Park, NC 27709, USA
 Phone: +1 919-254-4358
 Fax:   +1 919-254-6243
 EMail: dudleyg@us.ibm.com

Dudley Informational [Page 44] RFC 2353 APPN/HPR in IP Networks May 1998

6.0 Appendix - Packet Format

6.1 HPR Use of IP Formats

+———————————————————————-+

6.1.1 IP Format for LLC Commands and Responses
The formats described here are used for the
following LLC commands and responses: XID
command and response, TEST command and response,
DISC command, and DM response.

+———————————————————————-+

+———————————————————————-+

IP Format for LLC Commands and Responses

+——-+—–+——————————————————–+

Byte Bit Content

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

0-p IP header (see note 1)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+1- UDP header (see note 2)
p+8

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+9- IEEE 802.2 LLC header (see note 3)
              _____________________
p+11

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+9 DSAP: same as for the base APPN (i.e., X'04' or an
installation-defined value)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+10 SSAP: same as for the base APPN (i.e., X'04' or an
installation-defined value)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+11 Control: set as appropriate

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+12-n Remainder of PDU: XID3 or TEST information field, or
null for DISC command and DM response

+——-+—–+——————————————————–+

Dudley Informational [Page 45] RFC 2353 APPN/HPR in IP Networks May 1998

+——-+—–+——————————————————–+

Note 1: Rules for encoding the IP header can be found
in RFC 791.

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

Note 2: Rules for encoding the UDP header can be
found in RFC 768.

+——-+—–+——————————————————–+

+———————————————————————-+

IP Format for LLC Commands and Responses

+——-+—–+——————————————————–+

Byte Bit Content

+——-+—–+——————————————————–+

+——-+—–+——————————————————–+

Note 3: Rules for encoding the IEEE 802.2 LLC header
can be found in ISO/IEC 8802-2:1994 (ANSI/IEEE Std
802.2, 1994 Edition), Information technology -
Telecommunications and information exchange between
systems - Local and metropolitan area networks -
Specific requirements - Part 2: Logical Link Control.

+——-+—–+——————————————————–+

+———————————————————————-+

6.1.2 IP Format for NLPs in UI Frames
This format is used for either LDLC specific
messages or HPR session and control traffic.

+———————————————————————-+ +———————————————————————-+

IP Format for NLPs in UI Frames

+——-+—–+——————————————————–+

Byte Bit Content

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

0-p IP header (see note 1)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+1- UDP header (see note 2)
p+8

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+9- IEEE 802.2 LLC header
              _____________________
p+11

+——-+—–+——————————————————–+

Dudley Informational [Page 46] RFC 2353 APPN/HPR in IP Networks May 1998

+——-+—–+——————————————————–+

p+9 DSAP: the destination SAP obtained from the IEEE
802.2 LLC (X'80') subfield in the HPR Capabilities
(X'61') control vector in the received XID3 (see note
3)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+10 SSAP: the source SAP obtained from the IEEE 802.2 LLC
(X'80') subfield in the HPR Capabilities (X'61')
control vector in the sent XID3 (see note 4)

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

p+11 Control:

+——-+—–+——-+————————————————+

X'03' UI with P/F bit off

+——-+—–+——-+————————————————+ +——-+—–+——————————————————–+

p+12-n Remainder of PDU: NLP

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

Note 1: Rules for encoding the IP header can be found
in RFC 791.

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

Note 2: Rules for encoding the UDP header can be
found in RFC 768.

+——-+—–+——————————————————–+ +———————————————————————-+

IP Format for NLPs in UI Frames

+——-+—–+——————————————————–+

Byte Bit Content

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

Note 3: The User-Defined Address bit is considered
part of the DSAP. The Individual/Group bit in the
DSAP field is set to 0 by the sender and ignored by
the receiver.

+——-+—–+——————————————————–+ +——-+—–+——————————————————–+

Note 4: The User-Defined Address bit is considered
part of the SSAP. The Command/Response bit in the
SSAP field is set to 0 by the sender and ignored by
the receiver.

+——-+—–+——————————————————–+

Dudley Informational [Page 47] RFC 2353 APPN/HPR in IP Networks May 1998

7.0 Full Copyright Statement

Copyright (C) The Internet Society (1997). All Rights Reserved.

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Dudley Informational [Page 48]

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