GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc4562

Network Working Group T. Melsen Request for Comments: 4562 S. Blake Category: Informational Ericsson

                                                             June 2006
                       MAC-Forced Forwarding:
  A Method for Subscriber Separation on an Ethernet Access Network

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 (2006).

Abstract

 This document describes a mechanism to ensure layer-2 separation of
 Local Area Network (LAN) stations accessing an IPv4 gateway over a
 bridged Ethernet segment.
 The mechanism - called "MAC-Forced Forwarding" - implements an
 Address Resolution Protocol (ARP) proxy function that prohibits
 Ethernet Media Access Control (MAC) address resolution between hosts
 located within the same IPv4 subnet but at different customer
 premises, and in effect directs all upstream traffic to an IPv4
 gateway.  The IPv4 gateway provides IP-layer connectivity between
 these same hosts.

Melsen & Blake Informational [Page 1] RFC 4562 MAC-Forced Forwarding June 2006

Table of Contents

 1. Introduction ....................................................2
    1.1. Access Network Requirements ................................3
    1.2. Using Ethernet as an Access Network Technology .............4
 2. Terminology .....................................................5
 3. Solution Aspects ................................................6
    3.1. Obtaining the IP and MAC Addresses of the Access Routers ...6
    3.2. Responding to ARP Requests .................................7
    3.3. Filtering Upstream Traffic .................................8
    3.4. Restricted Access to Application Servers ...................8
 4. Access Router Considerations ....................................8
 5. Resiliency Considerations .......................................9
 6. Multicast Considerations ........................................9
 7. IPv6 Considerations ............................................10
 8. Security Considerations ........................................10
 9. Acknowledgements ...............................................11
 10. References ....................................................11
    10.1. Normative References .....................................11
    10.2. Informative References ...................................12

1. Introduction

 The main purpose of an access network is to provide connectivity
 between customer hosts and service provider access routers (ARs),
 typically offering reachability to the Internet and other IP networks
 and/or IP-based applications.
 An access network may be decomposed into a subscriber line part and
 an aggregation network part.  The subscriber line - often referred to
 as "the first mile" - is characterized by an individual physical (or
 logical, in the case of some wireless technologies) connection to
 each customer premises.  The aggregation network - "the second mile"
 - performs aggregation and concentration of customer traffic.
 The subscriber line and the aggregation network are interconnected by
 an Access Node (AN).  Thus, the AN constitutes the border between
 individual subscriber lines and the common aggregation network.  This
 is illustrated in the following figure.

Melsen & Blake Informational [Page 2] RFC 4562 MAC-Forced Forwarding June 2006

      Access       Aggregation  Access    Subscriber    Customer
      Routers      Network      Nodes     Lines         Premises
                                                        Networks
      +----+           |
    --+ AR +-----------|        +----+
      +----+           |        |    +----------------[]--------
                       |--------+ AN |
                       |        |    +----------------[]--------
                       |        +----+
                       |
                       |        +----+
                       |        |    +----------------[]--------
                       |--------+ AN |
                       |        |    +----------------[]--------
                       |        +----+
                       |
                       |        +----+
                       |        |    +----------------[]--------
                       |--------+ AN |
      +----+           |        |    +----------------[]--------
    --+ AR +-----------|        +----+
      +----+           |

1.1. Access Network Requirements

 There are two basic requirements that an access network solution must
 satisfy:
 1. Layer-2 separation between customer premises.
 2. High IPv4 address assignment efficiency.
 It is required that all traffic to and from customer hosts located at
 different premises (i.e., accessed via different subscriber lines or
 via different access networks) be forwarded via an AR, and not
 bridged or switched at layer-2 (Requirement 1; see also requirement
 R-40 in [TR101]).  This enables the access network service provider
 to use the AR(s) to perform security filtering, policing, and
 accounting of all customer traffic.  This implies that within the
 access network, layer-2 traffic paths should not exist that
 circumvent an AR (with some exceptions; see Section 3.4).
 In ATM-based access networks, the separation of individual customer
 hosts' traffic is an intrinsic feature achieved by the use of ATM
 permanent virtual connections (PVCs) between the customers' access
 device (e.g., DSL modem) and the AR (typically co-located/integrated
 with access control functionality in a Broadband Remote Access Server

Melsen & Blake Informational [Page 3] RFC 4562 MAC-Forced Forwarding June 2006

 (BRAS)).  In this case, the AN is an ATM-based Digital Subscriber
 Line Access Multiplexer (DSLAM).
 This document, however, targets Ethernet-based access networks.
 Techniques other than ATM PVCs must be employed to ensure the desired
 separation of traffic to and from individual customer hosts.
 Efficient address assignment is necessary to minimize consumption of
 the scarce IPv4 address space (Requirement 2).  See [RFC3069] for
 further discussion.  Address assignment efficiency is improved if
 host addresses are assigned out of one or more large pools, rather
 than by being assigned out of separate, smaller subnet blocks
 allocated to each customer premises.  IPv6 address assignment
 efficiency is of much less concern, and it is anticipated that IPv6
 deployments will allocate separate IPv6 subnet blocks to each
 customer premises [v6BB].

1.2. Using Ethernet as an Access Network Technology

 A major aspect of using Ethernet as an access technology is that
 traffic pertaining to different customer hosts is conveyed over a
 shared broadcast network.  Layer-2 isolation between customer
 premises networks could be provided by implementing access router
 functionality in each EAN, treating each subscriber line as a
 separate IP interface.  However, there are a variety of reasons why
 it is often desirable to avoid IP routing in the access network,
 including the need to satisfy regulatory requirements for direct
 layer-2 accessibility to multiple IP service providers.  In addition,
 this solution would not solve Requirement 2.
 To avoid IP routing within the access network, the Ethernet
 aggregation network is bridged via EANs to individual Ethernet
 networks at the customers' premises.  If the EANs were standard
 Ethernet bridges, then there would be direct layer-2 visibility
 between Ethernet stations (hosts) located at different customers'
 premises.  Specifically, hosts located within the same IP subnet
 would have this visibility.  This violates Requirement 1 (Section
 1.1) and introduces security issues, as malicious end-users thereby
 can attack hosts at other customers' premises directly at the
 Ethernet layer.
 Existing standardized solutions may be deployed to prevent layer-2
 visibility between stations:
 o  PPP over Ethernet [RFC2516].  The use of PPPoE creates individual
    PPP sessions between hosts and one or more BRASes over a bridged
    Ethernet topology.  Traffic always flows between a BRAS and hosts,

Melsen & Blake Informational [Page 4] RFC 4562 MAC-Forced Forwarding June 2006

    never directly between hosts.  The AN can force upstream traffic
    to flow only to the BRAS initially selected by the host.
 o  VLAN per-customer premises network [RFC3069].  Traffic to/from
    each customer premises network can be separated into different
    VLANs across the aggregation network between the AN and the AR.
 Both solutions provide layer-2 isolation between customer hosts, but
 they are not considered optimal for broadband access networks,
 because:
 o  PPPoE does not support efficient multicast: packets must be
    replicated on each PPPoE session to hosts listening on a specific
    multicast group.  This negates one of the major advantages of
    using Ethernet (instead of ATM) as an access technology.  This is
    an especially problematic limitation for services such as IPTV,
    which require high bandwidth per-multicast group (channel), and
    which may often have hundreds or thousands of listening customer
    hosts per group.
 o  Using VLANs to isolate individual customer premises networks also
    forces multicast packets to be replicated to each VLAN with a
    listening host.  Furthermore, the basic limit of a maximum of 4096
    VLANs per-Ethernet network limits the scalability of the solution.
    This scalability limit can be removed by deploying VLAN stacking
    techniques within the access network, but this approach increases
    provisioning complexity.
 The solution proposed in this document avoids these problems.

2. Terminology

 Access Node (AN)
    The entity interconnecting individual subscriber lines to the
    shared aggregation network.
 Access Router (AR)
    The entity interconnecting the access network to the Internet or
    other IP-based networks.  The AR provides connectivity between
    hosts on the access network at different customer premises.  It is
    also used to provide security filtering, policing, and accounting
    of customer traffic.
 Application Server (AS)
    A server, usually owned by a service provider, that attaches
    directly to the aggregation network and is directly reachable at
    layer-2 by customer hosts.

Melsen & Blake Informational [Page 5] RFC 4562 MAC-Forced Forwarding June 2006

 Ethernet Access Node (EAN)
    An Access Node supporting Ethernet-based subscriber lines and
    uplinks to an Ethernet-based aggregation network and MAC-Forced
    Forwarding.  For example, for xDSL access, the EAN is an
    Ethernet-centric DSLAM.  The EAN is a special type of filtering
    bridge that does not forward Ethernet broadcast and multicast
    frames originating on a subscriber line to other subscriber lines,
    but either discards them or forwards them upstream (towards the
    aggregation network).  The EAN also discards unicast Ethernet
    frames that originate on a subscriber line and are not addressed
    to an AR.

3. Solution Aspects

 The basic property of the solution is that the EAN ensures that
 upstream traffic is always sent to a designated AR, even if the IP
 traffic should ultimately flow between customer hosts located within
 the same IP subnet.
 The solution has three major aspects:
 1. Initially, the EAN obtains the IP and MAC addresses of the allowed
    target ARs for each customer host.
 2. The EAN replies to any upstream ARP request [RFC0826] from
    customer hosts with the MAC address of an allowed target AR.
 3. The EAN discards any upstream unicast traffic to MAC addresses
    other than the allowed target ARs.  The EAN also discards all
    non-essential broadcast and multicast packets received on
    subscriber lines.
 These aspects are discussed in the following sections.

3.1. Obtaining the IP and MAC Addresses of the Access Routers

 An access network may contain multiple ARs, and different hosts may
 be assigned to different (groups of) ARs.  This implies that the EAN
 must register the assigned AR addresses on a per-customer host basis.
 For each customer host, one of the ARs is acting as the default
 gateway.  If a customer has simultaneous access to multiple ARs, the
 other ARs typically will provide access to other IP networks.
 The EAN learns the IPv4 address of the allowed target ARs in one of
 two ways, depending on the host IPv4 address assignment method.  For
 each host using Dynamic Host Configuration Protocol (DHCP), the EAN
 learns the AR IPv4 addresses dynamically by snooping the DHCPACK

Melsen & Blake Informational [Page 6] RFC 4562 MAC-Forced Forwarding June 2006

 reply to a host [RFC2131].  If a host using DHCP shall have
 simultaneous access to multiple ARs, DHCP option 121 [RFC3442] or
 DHCP option 33 [RFC2132] must be used to specify them for that host.
 If static address assignment is used instead of DHCP, then AR IPv4
 addresses must be pre-provisioned in the EAN by the network operator.
 In both cases, the EAN will ARP to determine the ARs' corresponding
 MAC addresses.  This can be done immediately after the IPv4 addresses
 are learned or when the MAC addresses are first required.
 The DHCP server can associate customer hosts with subscriber lines if
 the EAN uses the DHCP Relay Agent Information Option (82) to convey a
 subscriber line identifier to the DHCP server in DHCP messages
 flowing upstream from the customer host [RFC3046].

3.2. Responding to ARP Requests

 If all customer networks were assigned individual IP subnet blocks
 (and if routing protocols were blocked inside the access network),
 then all upstream traffic would normally go to an AR (typically the
 default gateway), and the EAN could validate all upstream traffic by
 checking that the destination MAC address matched that of an AR.
 However, to comply with Requirement 2 of Section 1.1, residential
 customer networks are not (usually) assigned individual IPv4 subnet
 blocks.  In other words, several hosts located at different premises
 are within the same IPv4 subnet.  Consequently, if a host wishes to
 communicate with a host at another premises, an ARP request is issued
 to obtain that host's corresponding MAC address.  This request is
 intercepted by the EAN's ARP proxy, and an ARP reply is sent,
 specifying an allowed AR MAC address (typically the default
 gateway's) as the requested layer-2 destination address, in a manner
 similar to the "proxy ARP" mechanism described in [RFC1812].  In this
 way, the ARP table of the requesting host will register an AR MAC
 address as the layer-2 destination for any host within that IPv4
 subnet (except those at the same customer premises; see below).
 ARP requests for an IPv4 address of an allowed target AR are replied
 to by the EAN's ARP proxy with that AR's MAC address, rather than the
 MAC address of the default gateway AR.
 An exception is made when a host is ARPing for another host located
 within the same premises network.  If this ARP request reaches the
 EAN, it should be discarded, because it is assumed to be answered
 directly by the target host within the premises network.  The EAN
 must keep track of all assigned IPv4 addresses on a subscriber line
 so that it can detect these ARP requests and discard them.

Melsen & Blake Informational [Page 7] RFC 4562 MAC-Forced Forwarding June 2006

3.3. Filtering Upstream Traffic

 Since the EAN's ARP proxy will always reply with the MAC address of
 an AR, the requesting host will never learn MAC addresses of hosts
 located at other premises.  However, malicious customers or
 malfunctioning hosts may still try to send traffic using other
 unicast destination MAC addresses.  The EAN must discard all unicast
 frames received on a subscriber line that are not addressed to a
 destination MAC address for an allowed AR (with some exceptions; see
 Section 3.4.
 Similarly, broadcast or multicast packets received on a subscriber
 line must never be forwarded on other subscriber lines, but only on
 EAN uplinks to the aggregation network.  An EAN must discard all
 non-ARP broadcast packets received on subscriber lines, except when
 DHCP is in use, in which case, the EAN must forward client-to-server
 DHCP broadcast messages (DHCPDISCOVER, DHCPREQUEST, DHCPDECLINE,
 DHCPINFORM) [RFC2131] upstream.  An EAN should rate limit upstream
 broadcast packets.
 Broadcast packets forwarded on an EAN uplink may be forwarded to
 other EANs by the aggregation network.  EANs should discard all
 broadcast packets received from the aggregation network, except ARPs
 from ARs for subscriber hosts and server-to-client DHCP messages
 (DHCPOFFER, DHCPACK, DHCPNAK) [RFC2131], when DHCP is in use.
 Filtering of multicast packets to and from an EAN uplink is discussed
 in Section 6.

3.4. Restricted Access to Application Servers

 The previous discussion (Section 3.1) describes how customer hosts
 are allowed direct layer-2 connectivity only to one or more ARs.
 Similarly, a customer host could be allowed direct layer-2 access to
 one or more Application Servers (ASes) which are directly connected
 to the aggregation network.  There is no functional difference in the
 way MAC-Forced Forwarding treats access to ARs and ASes.

4. Access Router Considerations

 Traffic between customer hosts that belong to the same IPv4 subnet
 but are located at different customer premises will always be
 forwarded via an AR.  In this case, the AR will forward the traffic
 to the originating network, i.e., on the same interface from where it
 was received.  This normally results in an ICMP redirect message
 [RFC0792] being sent to the originating host.  To prevent this
 behavior, the ICMP redirect function for aggregation network
 interfaces must be disabled in the AR.

Melsen & Blake Informational [Page 8] RFC 4562 MAC-Forced Forwarding June 2006

5. Resiliency Considerations

 The operation of MAC-Forced Forwarding does not interfere with or
 delay IP connectivity recovery in the event of a sustained AR
 failure.  Use of DHCP to configure hosts with information on
 multiple, redundant ARs, or use of Virtual Router Redundancy Protocol
 (VRRP) [RFC3768] to implement AR redundancy, allows IP connectivity
 to be maintained.
 MAC-Forced Forwarding is a stateful protocol.  If static IPv4 address
 assignment is used in the access network, then the EAN must be pre-
 provisioned with state information for the customer hosts which may
 be reached via a subscriber line, and the ARs associated with those
 hosts.  In the event of a transient EAN failure, the EAN's state
 database can be quickly recovered from its configuration storage.
 If DHCP is used to assign IPv4 addresses in the access network, then
 MAC-Forced Forwarding operates as a soft-state protocol.  Since the
 DHCP and ARP messages that are snooped to construct the EAN state
 database are usually sent infrequently, a transient failure may not
 be detected by either the AR(s) or the customer hosts.  Therefore, a
 transient failure of an EAN could lead to an extended loss of
 connectivity.  To minimize connectivity loss, an EAN should maintain
 its dynamic state database in resilient storage to permit timely
 database and connectivity restoration.
 The EAN is a single point of attachment between a subscriber line and
 the aggregation network; hence, the EAN is a single point of
 connectivity failure.  Customers seeking more resilient connectivity
 should multi-home.

6. Multicast Considerations

 Multicast traffic delivery for streams originating within the
 aggregation network or further upstream and delivered to one or more
 customer hosts in an access network is supported in a scalable manner
 by virtue of Ethernet's native multicast capability.  Bandwidth
 efficiency can be enhanced if the EAN behaves as an IGMP snooping
 bridge; e.g., if it snoops on IGMP Membership Report and Leave Group
 messages originating on subscriber lines to prune the set of
 subscriber lines on which to forward particular multicast groups
 [RFC3376].
 An EAN must discard all IPv4 multicast packets received on a
 subscriber line other than IGMP Membership Report and Leave Group
 messages [RFC3376].  If a customer host wishes to source multicast
 packets to a group, the host must tunnel them upstream to a multicast
 router; e.g., an AR acting as a Protocol Independent Multicast -

Melsen & Blake Informational [Page 9] RFC 4562 MAC-Forced Forwarding June 2006

 Sparse Mode (PIM-SM) Designated Router [RFC2362].  An AR will forward
 them back into the access network if there are any listening customer
 hosts.
 EAN processing of IPv6 multicast packets is discussed in the next
 section.

7. IPv6 Considerations

 MAC-Forced Forwarding is not directly applicable for IPv6 access
 networks for the following reasons:
 1. IPv6 access networks do not require the same efficiency of address
    allocation as IPv4 access networks.  It is expected that customer
    premises networks will be allocated unique network prefixes (e.g.,
    /48) accommodating large numbers of customer subnets and hosts
    [v6BB].
 2. IPv6 nodes do not use ARP, but instead use the Neighbor Discovery
    Protocol [RFC2461] for layer-2 address resolution.
 To simultaneously support both IPv6 and MAC-Forced Forwarding for
 IPv4, an EAN can implement the unicast, broadcast, and multicast
 filtering rules described in Section 3.3.  To correctly perform
 unicast filtering, the EAN must learn the IPv6 and MAC addresses of
 the allowed ARs for a particular subscriber line.  It can learn these
 addresses either through static configuration or by snooping Router
 Discovery messages exchanged between the customer premises router and
 one or more ARs [RFC2461].
 Multicast is an intrinsic part of the IPv6 protocol suite.
 Therefore, an EAN must not indiscriminately filter IPv6 multicast
 packets flowing upstream, although it may rate limit them.  Detailed
 IPv6 multicast filtering rules are not discussed in this document.

8. Security Considerations

 MAC-Forced Forwarding is, by its nature, a security function,
 ensuring layer-2 isolation of customer hosts sharing a broadcast
 access medium.  In that sense, it provides security equivalent to
 alternative PVC-based solutions.  Security procedures appropriate for
 any shared access medium are equally appropriate when MAC-Forced
 Forwarding is employed.  It does not introduce any additional
 vulnerabilities over those of standard Ethernet bridging.
 In addition to layer-2 isolation, an EAN implementing MAC-Forced
 Forwarding must discard all upstream broadcast packets, except for
 valid DHCP messages, and ARP requests (which are proxied by the EAN).

Melsen & Blake Informational [Page 10] RFC 4562 MAC-Forced Forwarding June 2006

 In particular, the EAN must discard any DHCP server replies
 originating on a subscriber line.  Further, an EAN may rate limit
 upstream broadcast DHCP messages.
 An EAN implementing MAC-Forced Forwarding must keep track of IPv4
 addresses allocated on subscriber lines.  Therefore, the EAN has
 sufficient information to discard upstream traffic with spoofed IPv4
 source addresses.

9. Acknowledgements

 The authors would like to thank Ulf Jonsson, Thomas Narten, James
 Carlson, Rolf Engstrand, Tomas Thyni, and Johan Kolhi for their
 helpful comments.

10. References

10.1. Normative References

 [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
            RFC 792, September 1981.
 [RFC0826]  Plummer, D., "Ethernet Address Resolution Protocol:  Or
            converting network protocol addresses to 48.bit Ethernet
            address for transmission on Ethernet hardware", STD 37,
            RFC 826, November 1982.
 [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
            2131, March 1997.
 [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
            Extensions", RFC 2132, March 1997.
 [RFC2362]  Estrin, D., Farinacci, D., Helmy, A., Thaler, D., Deering,
            S., Handley, M., Jacobson, V., Liu, C., Sharma, P., and L.
            Wei, "Protocol Independent Multicast-Sparse Mode (PIM-SM):
            Protocol Specification", RFC 2362, June 1998.
 [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option", RFC
            3046, January 2001.
 [RFC3376]  Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
            Thyagarajan, "Internet Group Management Protocol, Version
            3", RFC 3376, October 2002.
 [RFC3442]  Lemon, T., Cheshire, S., and B. Volz, "The Classless
            Static Route Option for Dynamic Host Configuration
            Protocol (DHCP) version 4", RFC 3442, December 2002.

Melsen & Blake Informational [Page 11] RFC 4562 MAC-Forced Forwarding June 2006

10.2. Informative References

 [RFC1812]  Baker, F., "Requirements for IP Version 4 Routers", RFC
            1812, June 1995.
 [RFC3768]  Hinden, R., "Virtual Router Redundancy Protocol (VRRP)",
            RFC 3768, April 2004.
 [RFC2461]  Narten, T., Nordmark, E., and W. Simpson, "Neighbor
            Discovery for IP Version 6 (IPv6)", RFC 2461, December
            1998.
 [RFC2516]  Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D.,
            and R. Wheeler, "A Method for Transmitting PPP Over
            Ethernet (PPPoE)", RFC 2516, February 1999.
 [RFC3069]  McPherson, D. and B. Dykes, "VLAN Aggregation for
            Efficient IP Address Allocation", RFC 3069, February 2001.
 [TR101]    DSL Forum, "Migration to Ethernet-Based DSL Aggregation",
            Technical Report TR-101, April 2006.
 [v6BB]     Asadullah, S., Ahmed, A., Popoviciu, C., Savola, P., and
            J.  Palet, "ISP IPv6 Deployment Scenarios in Broadband
            Access Networks", Work in Progress.

Authors' Addresses

 Torben Melsen
 Ericsson
 Faelledvej
 Struer  DK-7600
 Denmark
 EMail: Torben.Melsen@ericsson.com
 Steven Blake
 Ericsson
 920 Main Campus Drive
 Suite 500
 Raleigh, NC  27606
 USA
 Phone: +1 919 472 9913
 EMail: steven.blake@ericsson.com

Melsen & Blake Informational [Page 12] RFC 4562 MAC-Forced Forwarding June 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78 and at www.rfc-editor.org/copyright.html, and
 except as set forth therein, the authors retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM 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.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Melsen & Blake Informational [Page 13]

/data/webs/external/dokuwiki/data/pages/rfc/rfc4562.txt · Last modified: 2006/06/09 22:02 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki