Internet DRAFT - draft-ietf-mpls-tp-ethernet-addressing
draft-ietf-mpls-tp-ethernet-addressing
MPLS D. Frost
Internet-Draft S. Bryant
Intended status: Standards Track Cisco Systems
Expires: January 25, 2014 M. Bocci
Alcatel-Lucent
July 24, 2013
MPLS-TP Next-Hop Ethernet Addressing
draft-ietf-mpls-tp-ethernet-addressing-08
Abstract
The Multiprotocol Label Switching (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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 25, 2014.
Copyright Notice
Copyright (c) 2013 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
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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 only optional in an MPLS-TP network, IP-based
protocols for Media Access Control (MAC) address learning, such as
the Address Resolution Protocol (ARP) [RFC0826] and IP version 6
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 dataplane.
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
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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
of the presence of the Ethernet Address Resolution Protocol (commonly
referred to as Address Resolution Protocol and shortened to
ARP)[RFC0826] or IP version 6 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
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 MAC address learning mechanism
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 which 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 MPLS packets received from a point-to-point Ethernet link
with this destination MAC address to the MPLS sub-system.
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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
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 which 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) [I-D.ietf-mpls-gach-adv]
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 [I-D.ietf-mpls-gach-adv] Section 7). 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" (TBD1), 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 [I-D.ietf-mpls-gach-adv]:
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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.
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 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: 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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MFS Object Format
Per [I-D.ietf-mpls-gach-adv], 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
have been disconnected from its peer send a GAP Ethernet Interface
Parameter message, and that it issues a GAP request message for the
Ethernet parameters at the earliest opportunity.
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When the MAC address in the received Source MAC Address TLV changes
the new MAC address MUST be used (see Section 5.2 of
[I-D.ietf-mpls-gach-adv]).
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 the link, thereby triggering a fault,
and hence 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 the received information, it MUST be clear why the
configured value has been changed. The information being advertised
SHOULD be persistent across restarts. To ensure correct operation
when an equipment restarts in a new environment, previously received
advertisements MUST be discarded across restarts. If the received
values change, the new values MUST be used and the change made
visible to the network operators.
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 addressing Ethernet 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
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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.
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 [I-D.ietf-mpls-gach-adv]
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 is requested to update the reference to
point to the RFC number assigned to this document.
7.2. G-ACh Advertisement Protocol Allocation
IANA is requested to allocate a new Application ID in the "G-ACh
Advertisement Protocol Applications" registry
[I-D.ietf-mpls-gach-adv] (currently located in the "Pseudowire Name
Spaces (PWE3)"), as follows:
Application ID Description Reference
------------------------- --------------------------- ---------------
TBD1 to be assigned by Ethernet Interface (this draft)
IANA Parameters
7.3. Creation of Ethernet Interface Parameters Registry
IANA is requested to create a new registry, "G-ACh Advertisement
Protocol: Ethernet Interface Parameters" within the "Pseudowire Name
Spaces (PWE3)" with fields and initial allocations as follows:
Type Name Type ID Reference
------------------ ------- ------------
Source MAC Address 0 (this draft)
Maximum Frame Size 1 (this draft)
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The range of the Type ID field is 0 - 255.
The allocation policy for this registry is IETF Review or IESG
approval.
8. Acknowledgements
We thank Adrian Farrel for his valuable review comments on this
document.
9. References
9.1. Normative References
[EUI-64] , "[EUI64] IEEE, "Guidelines for 64-bit Global Identifier
(EUI-64) Registration Authority", http://
standards.ieee.org/regauth/oui/tutorials/EUI64.html, March
1997.", .
[I-D.ietf-mpls-gach-adv]
Frost, D., Bryant, S., and M. Bocci, "MPLS Generic
Associated Channel (G-ACh) Advertisement Protocol", draft-
ietf-mpls-gach-adv-08 (work in progress), June 2013.
[LLDP] , "IEEE, "Station and Media Access Control Connectivity
Discovery (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.
9.2. Informative References
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
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address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[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.
Authors' Addresses
Dan Frost
Cisco Systems
Email: danfrost@cisco.com
Stewart Bryant
Cisco Systems
Email: stbryant@cisco.com
Matthew Bocci
Alcatel-Lucent
Email: matthew.bocci@alcatel-lucent.com
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