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rfc:rfc7213

Internet Engineering Task Force (IETF) D. Frost Request for Comments: 7213 Blue Sun Category: Standards Track S. Bryant ISSN: 2070-1721 Cisco Systems

                                                              M. Bocci
                                                        Alcatel-Lucent
                                                             June 2014
   MPLS Transport Profile (MPLS-TP) Next-Hop Ethernet Addressing

Abstract

 The MPLS Transport Profile (MPLS-TP) is the set of MPLS protocol
 functions applicable to the construction and operation of packet-
 switched transport networks.  This document presents considerations
 for link-layer addressing of Ethernet frames carrying MPLS-TP
 packets.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7213.

Copyright Notice

 Copyright (c) 2014 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Frost, et al. Standards Track [Page 1] RFC 7213 MPLS-TP Ethernet Addressing June 2014

1. Introduction

 The MPLS Transport Profile (MPLS-TP) [RFC5921] is the set of protocol
 functions that meet the requirements [RFC5654] for the application of
 MPLS to the construction and operation of packet-switched transport
 networks.  The MPLS-TP data plane consists of those MPLS-TP functions
 concerned with the encapsulation and forwarding of MPLS-TP packets
 and is described in [RFC5960].
 This document presents considerations for link-layer addressing of
 Ethernet frames carrying MPLS-TP packets.  Since MPLS-TP packets are
 MPLS packets, existing procedures ([RFC3032], [RFC5332]) for the
 encapsulation of MPLS packets over Ethernet apply.  Because IP
 functionality is optional in an MPLS-TP network, IP-based protocols
 for Media Access Control (MAC) address learning, such as the Address
 Resolution Protocol (ARP) [RFC826] and IPv6 Neighbor Discovery
 [RFC4861], may not be available.  This document specifies the options
 for the determination and selection of the next-hop Ethernet MAC
 address when MPLS-TP is used between nodes that do not have an IP
 data plane.

1.1. Terminology

 Term    Definition
 ------- ---------------------------
 ARP     Address Resolution Protocol
 G-ACh   Generic Associated Channel
 LSP     Label Switched Path
 LSR     Label Switching Router
 MAC     Media Access Control
 MPLS-TP MPLS Transport Profile
 Additional definitions and terminology can be found in [RFC5960] and
 [RFC5654].

1.2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

2. Point-to-Point Link Addressing

 When two MPLS-TP nodes are connected by a point-to-point Ethernet
 link, the question arises as to what destination Ethernet Media
 Access Control (MAC) address should be specified in Ethernet frames
 transmitted to the peer node over the link.  The problem of
 determining this address does not arise in IP/MPLS networks because

Frost, et al. Standards Track [Page 2] RFC 7213 MPLS-TP Ethernet Addressing June 2014

 of the presence of the Ethernet Address Resolution Protocol (commonly
 referred to as the Address Resolution Protocol and shortened to ARP)
 [RFC826] or IPv6 Neighbor Discovery (ND) protocol [RFC4861], which
 allow the unicast MAC address of the peer device to be learned
 dynamically.
 If existing mechanisms are available in an MPLS-TP network to
 determine the destination unicast MAC addresses of peer nodes, for
 example, if the network also happens to be an IP/MPLS network, or if
 the Link Layer Discovery Protocol (LLDP) [LLDP] is in use, these
 methods SHOULD be used.  If ARP, ND, and LLDP are not available, and
 both peers implement the procedures in Section 4 of this document,
 then the GAP mechanism described in this memo SHOULD be used.  The
 remainder of this section discusses alternative options that might be
 employed when none of the preceding mechanisms for learning MAC
 addresses are available.
 One common approach is for each node to be statically configured with
 the MAC address of its peer.  However, static MAC address
 configuration can present an administrative burden and lead to
 operational problems.  For example, replacement of an Ethernet
 interface to resolve a hardware fault when this approach is used
 requires that the peer node be manually reconfigured with the new MAC
 address.  This is especially problematic if the peer is operated by
 another provider.
 Another approach that may be considered is to use the Ethernet
 broadcast address FF-FF-FF-FF-FF-FF as the destination MAC address in
 frames carrying MPLS-TP packets over a link that is known to be
 point-to-point.  This may, however, lead to excessive frame
 distribution and processing at the Ethernet layer.  Broadcast traffic
 may also be treated specially by some devices, and this may not be
 desirable for MPLS-TP data frames.
 In view of the above considerations, this document recommends that,
 if a non-negotiated address is to be used, both nodes are configured
 to use as a destination MAC address an Ethernet multicast address
 reserved for MPLS-TP for use over point-to-point links.  The address
 allocated for this purpose by the Internet Assigned Numbers Authority
 (IANA) is 01-00-5E-90-00-00.  An MPLS-TP implementation MUST default
 to passing to the MPLS sub-system any MPLS packets received from a
 point-to-point Ethernet link with this destination MAC address.
 The use of broadcast or multicast addressing for the purpose
 described in this section, i.e., as a placeholder for the unknown
 unicast MAC address of the destination, is applicable only when the
 attached Ethernet link is known to be point-to-point.  If a link is
 not known to be point-to-point, these forms of broadcast or multicast

Frost, et al. Standards Track [Page 3] RFC 7213 MPLS-TP Ethernet Addressing June 2014

 addressing MUST NOT be used.  Thus, the implementation MUST provide a
 means for the operator to declare that a link is point-to-point if it
 supports these addressing modes.  Moreover, the operator is cautioned
 that it is not always clear whether a given link is, or will remain,
 strictly point-to-point, particularly when the link is supplied by an
 external provider; point-to-point declarations therefore need to be
 used with care.  Because of these caveats, it is RECOMMENDED that
 implementations support the procedures in Section 4 so that unicast
 addressing can be used.

3. Multipoint Link Addressing

 When a multipoint Ethernet link serves as a section [RFC5960] for a
 point-to-multipoint MPLS-TP LSP, and multicast destination MAC
 addressing at the Ethernet layer is used for the LSP, the addressing
 and encapsulation procedures specified in [RFC5332] SHALL be used.
 When a multipoint Ethernet link (that is, a link that is not known to
 be point-to-point) serves as a section for a point-to-point MPLS-TP
 LSP, unicast destination MAC addresses MUST be used for Ethernet
 frames carrying packets of the LSP.  According to the discussion in
 the previous section, this implies the use of either static MAC
 address configuration or a protocol that enables peer MAC address
 discovery.

4. MAC Address Discovery via the G-ACh Advertisement Protocol

 The G-ACh Advertisement Protocol (GAP) [RFC7212] provides a simple
 means of informing listeners on a link of the sender's capabilities
 and configuration.  When used for this purpose on an Ethernet link,
 GAP messages are multicast to the address 01-00-5e-80-00-0d (see
 Section 7 of [RFC7212]).  If these messages contain the unicast MAC
 address of the sender, then listeners can learn this address and use
 it in the future when transmitting frames containing MPLS-TP packets.
 Since the GAP does not rely on IP, this provides a means of unicast
 MAC discovery for MPLS-TP nodes without IP support.
 This document defines a new GAP application "Ethernet Interface
 Parameters" (0x0001) to support the advertisement of Ethernet-
 specific parameters associated with the sending interface.  The
 following Type-Length-Value (TLV) objects are defined for this
 application; the TLV format is as defined in [RFC7212]:
    Source MAC Address (type = 0, length = 8): The Value of this
    object is an EUI-64 [EUI-64] unicast MAC address assigned to one
    of the interfaces of the sender that is connected to this data
    link.  The IEEE-defined mapping from 48-bit MAC addresses to
    EUI-64 form is used.

Frost, et al. Standards Track [Page 4] RFC 7213 MPLS-TP Ethernet Addressing June 2014

    Maximum Frame Size (MFS) (type = 1, length = 4): The Value of this
    object is a 32-bit unsigned integer encoded in network byte order
    that specifies the maximum frame size in octets of an Ethernet
    Frame that can be sent over the sending interface.  Where MAC
    address learning occurs by some other means, this TLV group MAY be
    used to advertise only the MFS.  If multiple advertisements are
    made for the same parameter, use of these advertisements is
    undefined.
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Type=0    |    Reserved   |           Length=8            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                MAC Address in EUI-64 Format                   |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Source MAC Address Object Format
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type=1    |    Reserved   |          Length=4            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Maximum Frame Size (MFS)                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                           MFS Object Format
 Per [RFC7212], MAC address discovery information needs to be
 periodically retransmitted and is to be retained by a receiver based
 on the period of time indicated by the associated Lifetime field.  To
 expedite the initialization of a link, it is RECOMMENDED that a node
 that has been reconfigured, rebooted, or is aware that it has been
 disconnected from its peer send a GAP Ethernet Interface Parameters
 message, and that it issue a GAP Request message for the Ethernet
 Interface Parameters of its peers, at the earliest opportunity.
 When the MAC address in the received Source MAC Address TLV changes,
 the new MAC address MUST be used (see Section 5.2 of [RFC7212]).
 If a minimum MFS is configured for a link and the MFS advertised by
 the peer is lower than that minimum, the operator MUST be notified of
 the MFS mismatch.  Under these circumstances, the operator may choose
 to configure the LSR to shut down the link, thereby triggering a

Frost, et al. Standards Track [Page 5] RFC 7213 MPLS-TP Ethernet Addressing June 2014

 fault and causing the end-to-end path to be repaired.  Alternatively,
 the operator may choose to configure the LSR to leave the link up so
 that an OAM message can be used to verify the actual MFS.
 A peer node could cease transmission of G-ACh advertisements, or
 cease to include a Source MAC Address TLV in advertisements, or cease
 to be connected, any of which will cause the TLV lifetime to expire.
 After the Source MAC Address TLV lifetime has expired, this MAC
 Address MUST NOT be used as the peer MAC address.  The node MUST
 return to selecting MAC addresses as though no advertisements were
 received, using the method configured for this eventuality.

5. Manageability Considerations

 The values sent and received by this protocol MUST be made accessible
 for inspection by network operators, and where local configuration is
 updated by received information, it MUST be clear why the configured
 value has been changed.  If the received values change, the new
 values MUST be used and the change made visible to the network
 operators.
 The Ethernet address and associated parameters advertised for an
 interface SHOULD be persistent across restarts.  In the event of a
 system restart, any data that has been retained as a consequence of
 prior Ethernet Interface Parameters advertisements from GAP peers
 MUST be discarded; this prevents incorrect operation on the basis of
 stale data.
 Where the link changes to a new type, i.e., from point-to-point to
 point-to-multipoint, the network operator SHOULD be informed.  If the
 new link type is incompatible with the Ethernet addressing method in
 use, the system MUST take the action that is configured under those
 circumstances.

6. Security Considerations

 The use of broadcast or multicast Ethernet destination MAC addresses
 for frames carrying MPLS-TP data packets can potentially result in
 such frames being distributed to devices other than the intended
 destination node or nodes when the Ethernet link is not point-to-
 point.  The operator should take care to ensure that MPLS-TP nodes
 are aware of the Ethernet link type (point-to-point or multipoint).
 In the case of multipoint links, the operator should either ensure
 that no devices are attached to the link that are not authorized to
 receive the frames or take steps to mitigate the possibility of
 excessive frame distribution (for example, by configuring the
 Ethernet switch to appropriately restrict the delivery of multicast
 frames to authorized ports).

Frost, et al. Standards Track [Page 6] RFC 7213 MPLS-TP Ethernet Addressing June 2014

 An attacker could disrupt communications by modifying the Source MAC
 Address or the MFS values; however, this is mitigated by the use of
 cryptographic authentication as described in [RFC7212], which also
 describes other considerations applicable to the GAP protocol.
 Visibility into the contents of either of the TLVs could provide
 information that is useful for an attacker.  This is best addressed
 by physical security of the links.

7. IANA Considerations

7.1. Ethernet Multicast Address Allocation

 IANA has allocated an Ethernet multicast address from the "IANA
 Multicast 48-bit MAC Addresses" address block in the "Ethernet
 Numbers" registry for use by MPLS-TP LSRs over point-to-point links
 as described in Section 2.  The allocated address is
 01-00-5E-90-00-00.  IANA has updated the reference to point to the
 RFC number assigned to this document.

7.2. G-ACh Advertisement Protocol Allocation

 IANA has allocated a new Application ID in the "G-ACh Advertisement
 Protocol Application Registry", as follows:
 Application ID Description                   Reference
 -------------- ----------------------------- ---------
 0x0001         Ethernet Interface Parameters This RFC

7.3. Creation of Ethernet Interface Parameters Registry

 IANA has created a new registry, "G-ACh Advertisement Protocol:
 Ethernet Interface Parameters" within the "Generic Associated Channel
 (G-ACh) Parameters" registry with fields and initial allocations as
 follows:
 Type Name          Type ID Reference
 ------------------ ------- ---------
 Source MAC Address 0       This RFC
 Maximum Frame Size 1       This RFC
 The range of the Type ID field is 0 - 255.
 The allocation policy for this registry is IETF Review or IESG
 Approval.

Frost, et al. Standards Track [Page 7] RFC 7213 MPLS-TP Ethernet Addressing June 2014

8. Acknowledgements

 We thank Adrian Farrel for his valuable review comments on this
 document.

9. References

9.1. Normative References

 [EUI-64]   IEEE, "Guidelines for 64-bit Global Identifier (EUI-64)
            Registration Authority", March 1997,
            <http://standards.ieee.org/regauth/oui/tutorials/
            EUI64.html>.
 [LLDP]     IEEE, "Station and Media Access Control Connectivity
            Discovery", IEEE 802.1AB, September 2009.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
            Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
            Encoding", RFC 3032, January 2001.
 [RFC5332]  Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
            Multicast Encapsulations", RFC 5332, August 2008.
 [RFC5654]  Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
            and S. Ueno, "Requirements of an MPLS Transport Profile",
            RFC 5654, September 2009.
 [RFC5960]  Frost, D., Bryant, S., and M. Bocci, "MPLS Transport
            Profile Data Plane Architecture", RFC 5960, August 2010.
 [RFC7212]  Frost, D., Bryant, S., and M. Bocci, "MPLS Generic
            Associated Channel (G-ACh) Advertisement Protocol", RFC
            7212, June 2014.

9.2. Informative References

 [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
            "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
            September 2007.
 [RFC5921]  Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
            Berger, "A Framework for MPLS in Transport Networks", RFC
            5921, July 2010.

Frost, et al. Standards Track [Page 8] RFC 7213 MPLS-TP Ethernet Addressing June 2014

 [RFC826]   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.

Authors' Addresses

 Dan Frost
 Blue Sun
 EMail: frost@mm.st
 Stewart Bryant
 Cisco Systems
 EMail: stbryant@cisco.com
 Matthew Bocci
 Alcatel-Lucent
 EMail: matthew.bocci@alcatel-lucent.com

Frost, et al. Standards Track [Page 9]

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