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IETF RFC 7173
Last modified on Thursday, May 8th, 2014
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Internet Engineering Task Force (IETF) L. Yong
Request for Comments: 7173 D. Eastlake 3rd
Category: Standards Track S. Aldrin
ISSN: 2070-1721 Huawei
J. Hudson
Brocade
May 2014
Transparent Interconnection of Lots of Links (TRILL) Transport
Using Pseudowires
 Abstract
This document specifies how to interconnect a pair of Transparent
Interconnection of Lots of Links (TRILL) switch ports using
pseudowires under existing TRILL and Pseudowire Emulation End-to-End
(PWE3) standards.
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/RFC 7173.
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.
Yong, et al. Standards Track PAGE 1 
RFC 7173 PWE3 TRILL Transport May 2014
Table of Contents
1. Introduction.....................................................2
1.1. Conventions Used in This Document...........................2
2. PWE3 Interconnection of TRILL Switches...........................3
2.1. PWE3 Type-Independent Details...............................3
2.2. PPP PWE3 Transport of TRILL.................................4
3. Security Considerations..........................................6
Appendix A. Use of Other Pseudowire Types ..........................7
Acknowledgements ...................................................8
Normative References ...............................................9
Informative References ............................................10
1. Introduction
The Transparent Interconnection of Lots of Links (TRILL) protocol
[RFC 6325] provides optimal pair-wise data frame routing without
configuration in multi-hop networks with arbitrary topology. TRILL
supports multipathing of both unicast and multicast traffic. Devices
that implement TRILL are called TRILL switches or Routing Bridges
(RBridges).
Links between TRILL switches can be based on arbitrary link
protocols, for example, PPP [RFC 6361], as well as Ethernet [RFC 6325].
A set of connected TRILL switches together form a TRILL campus that
is bounded by end stations and Layer 3 routers.
This document specifies how to interconnect a pair of TRILL switch
ports using a pseudowire under existing TRILL and PWE3 (Pseudowire
Emulation End-to-End) standards.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC 2119].
Acronyms used in this document include the following:
IS-IS - Intermediate System to Intermediate System [IS-IS]
MPLS - Multi-Protocol Label Switching
PPP - Point-to-Point Protocol [RFC 1661]
PW - Pseudowire [RFC 3985]
Yong, et al. Standards Track PAGE 2
RFC 7173 PWE3 TRILL Transport May 2014
PWE3 - PW Emulation End-to-End
RBridge - Routing Bridge, an alternative name for a TRILL switch
TRILL - Transparent Interconnection of Lots of Links [RFC 6325]
TRILL Switch - A device implementing the TRILL protocol
2. PWE3 Interconnection of TRILL Switches
When a pseudowire is used to interconnect a pair of TRILL switch
ports, a PPP [RFC 4618] pseudowire is used as described below. The
pseudowire between such ports can be signaled [RFC 4447] or manually
configured. In this context, the TRILL switch ports at the ends of
the pseudowire are acting as native service processing (NSP) elements
[RFC 3985] and, assuming that the pseudowires are over MPLS or IP
[RFC 4023] networks, as label switched or IP routers at the TRILL
switch ports.
Pseudowires provide transparent transport, and the two TRILL switch
ports appear directly interconnected with a transparent link. With
such an interconnection, the TRILL adjacency over the link is
automatically discovered and established through TRILL IS-IS control
messages [RFC 7177].
A pseudowire is carried over a packet switched network tunnel
[RFC 3985], for example, an MPLS or MPLS-TP label switched path tunnel
in MPLS networks. Either a signaling protocol or manual
configuration can be used to configure a label switched path tunnel
between two TRILL switch ports. This application needs no additions
to the existing pseudowire standards.
2.1. PWE3 Type-Independent Details
The sending pseudowire TRILL switch port SHOULD map the inner
priority of the TRILL Data packets being sent to the Traffic Class
field of the pseudowire label [RFC 5462] so as to minimize the
probability that higher priority TRILL Data packets will be discarded
due to excessive TRILL Data packets of lower priority.
TRILL IS-IS PDUs critical to establishing and maintaining adjacency
(Hello and MTU PDUs) SHOULD be sent with the MPLS Traffic Class that
calls for handling with the maximum priority. Other TRILL IS-IS PDUs
SHOULD be sent with the MPLS Traffic Class denoting the highest
priority that is less than the maximum priority. TRILL Data packets
SHOULD be sent with appropriate MPLS Traffic Classes, typically
mapped from the TRILL Data packet priority, such that TRILL Data
packet Traffic Classes denote priorities less than the priorities
Yong, et al. Standards Track PAGE 3
RFC 7173 PWE3 TRILL Transport May 2014
used for TRILL IS-IS PDUs. This minimizes the probability of other
traffic interfering with these important control PDUs and causing
false loss of adjacency or other control problems.
If a pseudowire supports fragmentation and reassembly (a feature that
has received little or no deployment), then there is no reason to do
TRILL MTU testing on it, and the pseudowire will not be a constraint
on the TRILL campus-wide MTU size (Sz) (see Section 4.3.1 of
[RFC 6325]). If the pseudowire does not support fragmentation (the
more common case), then the available TRILL IS-IS packet payload size
over the pseudowire (taking into account MPLS encapsulation with a
control word) or some lower value, MUST be used in helping to
determine MTU size (Sz) (see Section 5 of [RFC 7180]).
An intervening MPLS label switched router or similar packet switched
network device has no awareness of TRILL. Such devices will not
change the TRILL Header hop count.
2.2. PPP PWE3 Transport of TRILL
For a PPP pseudowire (PW type = 0x0007), the two TRILL switch ports
being connected are configured to form a pseudowire with PPP
encapsulation [RFC 4618]. After the pseudowire is established and
TRILL use is negotiated within PPP, the two TRILL switch ports appear
directly connected with a PPP link [RFC 1661] [RFC 6361].
If pseudowire interconnection of two TRILL switch ports is signaled
[RFC 4447], the initiating TRILL switch port MUST attempt the
connection setup with pseudowire type PPP (0x0007).
Behavior for TRILL with a PPP pseudowire continues to follow that of
TRILL over PPP as specified in Section 3 of [RFC 6361].
Yong, et al. Standards Track PAGE 4
RFC 7173 PWE3 TRILL Transport May 2014
The following figures show what a TRILL Data packet and TRILL IS-IS
packet look like over such a pseudowire in the MPLS case, assuming no
TRILL Header extensions:
+--------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (4 octets per label)
+--------------------------------+
| PW Label | 4 octets
+--------------------------------+
| Control Word | 4 octets
+--------------------------------+
| PPP Header 0x005d | 2 octets
+--------------------------------+
| TRILL Header | 6 octets
+--------------------------------+
| Destination MAC Address | 6 octets
+--------------------------------+
| Source MAC Address | 6 octets
+--------------------------------+
| Data Label | 4 or 8 octets
+--------------------------------+
| Payload Body | variable
+--------------------------------+
Figure 1: TRILL Data Packet in Pseudowire
"Data Label" is the VLAN Label or Fine-Grained Label [RFC 7172] of the
payload.
+--------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (4 octets per label)
+--------------------------------+
| PW Label | 4 octets
+--------------------------------+
| Control Word | 4 octets
+--------------------------------+
| PPP Header 0x405d | 2 octets
+--------------------------------+
| Common IS-IS Header | 8 octets
+--------------------------------+
| IS-IS PDU Type Specific Header | variable
+--------------------------------+
| IS-IS TLVs | variable
+--------------------------------+
Figure 2: TRILL IS-IS Packet in Pseudowire
Yong, et al. Standards Track PAGE 5
RFC 7173 PWE3 TRILL Transport May 2014
The PPP Header fields (0x005d and 0x405d, respectively) for TRILL
Data and IS-IS packets shown above are specified in [RFC 6361].
3. Security Considerations
TRILL-level security mechanisms, such as the ability to use
authentication with TRILL IS-IS PDUs [RFC 6325], are not affected by
link technology, such as the use of pseudowire links as specified in
this document.
Link security may be useful in improving TRILL campus security.
TRILL is transported over pseudowires as TRILL over PPP over
pseudowires, pseudowires are over MPLS or IP, and MPLS and IP are
over some lower-level link technology. Thus, link security below the
TRILL level for a pseudowire link could be provided by PPP security,
pseudowire security, MPLS or IP security, or security of the link
technology supporting MPLS or IP.
PPP TRILL security considerations are discussed in [RFC 6361]. For
security considerations introduced by carrying PPP TRILL links over
pseudowires, see [RFC 3985], which discusses the risks introduced by
sending protocols that previously assumed a point-to-point link on a
pseudowire built on a packet switched network (PSN). However, the
PPP layer in TRILL transport by pseudowire is somewhat vestigial and
intended primarily as a convenient way to use existing PPP code
points to identify TRILL Data packets and TRILL IS-IS packets.
Furthermore, existing PPP security standards are arguably
questionable in terms of current security criteria. For these
reasons, it is NOT RECOMMENDED to use PPP security in the transport
of TRILL by pseudowires as specified in this document.
It is RECOMMENDED that link security be provided at the layers
supporting pseudowires transporting TRILL, that is, at the MPLS or IP
layer or the link layer transporting MPLS or IP.
For applications involving sensitive data, end-to-end security should
always be considered, in addition to link security, to provide
security in depth. In this context, such end-to-end security should
be between the end stations involved so as to protect the entire path
to, through, and from the TRILL campus.
For general TRILL protocol security considerations, see [RFC 6325].
Yong, et al. Standards Track PAGE 6
RFC 7173 PWE3 TRILL Transport May 2014
Appendix A. Use of Other Pseudowire Types
This informational appendix briefly discusses the use of pseudowire
types other than PPP for the transport of TRILL.
The use of Ethernet pseudowires [RFC 4448] was examined by the authors
and would be possible without change to such pseudowires; however,
this would require an additional 12 or 16 bytes per packet within the
payload being transmitted over the pseudowire for a TRILL Data packet
(Figure 3) and a TRILL IS-IS packet (Figure 4) over such an Ethernet
pseudowire in the MPLS case, assuming no TRILL Header extensions
(compare with Figures 1 and 2):
+--------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (4 octets per label)
+--------------------------------+
| PW Label | 4 octets
+--------------------------------+
| Optional Control Word | 4 octets
+--------------------------------+
| TRILL Hop Dest. MAC Address | 6 octets
+--------------------------------+
| TRILL Hop Source MAC Address | 6 octets
+--------------------------------+
|Optional VLAN and/or other tags | variable
+--------------------------------+
| TRILL Ethertype (0x22f3) | 2 octets
+--------------------------------+
| TRILL Header | 6 octets
+--------------------------------+
| Destination MAC Address | 6 octets
+--------------------------------+
| Source MAC Address | 6 octets
+--------------------------------+
| Data Label | 4 or 8 octets
+--------------------------------+
| Payload Body | variable
+--------------------------------+
Figure 3: TRILL Data Packet in Ethernet Pseudowire
"Data Label" is the VLAN Label or Fine-Grained Label [RFC 7172] of the
payload.
Yong, et al. Standards Track PAGE 7
RFC 7173 PWE3 TRILL Transport May 2014
+--------------------------------+
| Server MPLS Tunnel Label(s) | n*4 octets (4 octets per label)
+--------------------------------+
| PW Label | 4 octets
+--------------------------------+
| Optional Control Word | 4 octets
+--------------------------------+
| TRILL Hop Dest. MAC Address | 6 octets
+--------------------------------+
| TRILL Hop Source MAC Address | 6 octets
+--------------------------------+
|Optional VLAN and/or other tags | variable
+--------------------------------+
| Layer 2 IS-IS Ethertype 0x22f4 | 2 octets
+--------------------------------+
| Common IS-IS Header | 8 octets
+--------------------------------+
| IS-IS PDU Type Specific Header | variable
+--------------------------------+
| IS-IS TLVs | variable
+--------------------------------+
Figure 4: TRILL IS-IS Packet in Ethernet Pseudowire
It would also be possible to specify a new pseudowire type for TRILL
traffic, but the authors feel that any efficiency gain over PPP
pseudowires would be too small to be worth the complexity of adding
such a specification. Furthermore, using PPP pseudowire encoding
means that any traffic dissector that understands TRILL PPP encoding
[RFC 6361] and PPP pseudowires [RFC 4618] will automatically be able to
recursively decode TRILL transported by pseudowire.
Acknowledgements
Thanks for the valuable comments from the following, who are listed
in alphabetic order:
Stewart Bryant, Stephen Farrell, Brian Haberman, Christer
Holmberg, Joel Jaeggli, Barry Leiba, Erik Nordmark, Yaron Sheffer,
and Yaakov (J) Stein.
Yong, et al. Standards Track PAGE 8
RFC 7173 PWE3 TRILL Transport May 2014
Normative References
[RFC 1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
STD 51, RFC 1661, July 1994.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T., and
G. Heron, "Pseudowire Setup and Maintenance Using the
Label Distribution Protocol (LDP)", RFC 4447, April 2006.
[RFC 4618] Martini, L., Rosen, E., Heron, G., and A. Malis,
"Encapsulation Methods for Transport of PPP/High-Level
Data Link Control (HDLC) over MPLS Networks", RFC 4618,
September 2006.
[RFC 5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
[RFC 6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC 6361] Carlson, J. and D. Eastlake 3rd, "PPP Transparent
Interconnection of Lots of Links (TRILL) Protocol Control
Protocol", RFC 6361, August 2011.
[RFC 7172] Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
D. Dutt, "Transparent Interconnection of Lots of Links
(TRILL): Fine-Grained Labeling", RFC 7172, May 2014.
[RFC 7180] Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V., and
A. Banerjee, "Transparent Interconnection of Lots of Links
(TRILL): Clarifications, Corrections, and Updates",
RFC 7180, May 2014.
Yong, et al. Standards Track PAGE 9
RFC 7173 PWE3 TRILL Transport May 2014
Informative References
[IS-IS] ISO/IEC 10589:2002, Second Edition, "Information
technology -- Telecommunications and information exchange
between systems -- Intermediate System to Intermediate
System intra-domain routeing information exchange protocol
for use in conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)", 2002.
[RFC 3985] Bryant, S., Ed., and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC 4023] Worster, T., Rekhter, Y., and E. Rosen, Ed.,
"Encapsulating MPLS in IP or Generic Routing Encapsulation
(GRE)", RFC 4023, March 2005.
[RFC 4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G. Heron,
"Encapsulation Methods for Transport of Ethernet over MPLS
Networks", RFC 4448, April 2006.
[RFC 7177] Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
V. Manral, "Transparent Interconnection of Lots of Links
(TRILL): Adjacency", RFC 7177, May 2014.
Yong, et al. Standards Track PAGE 10
RFC 7173 PWE3 TRILL Transport May 2014
Authors' Addresses
Lucy Yong
Huawei Technologies
5340 Legacy Drive
Plano, TX 75024
USA
Phone: +1-469-227-5837
EMail: lucy.yong@huawei.com
Donald E. Eastlake 3rd
Huawei Technologies
155 Beaver Street
Milford, MA 01757
USA
Phone: +1-508-333-2270
EMail: d3e3e3@gmail.com
Sam Aldrin
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Phone: +1-408-330-4517
EMail: sam.aldrin@huawei.com
Jon Hudson
Brocade
130 Holger Way
San Jose, CA 95134
USA
Phone: +1-408-333-4062
EMail: jon.hudson@gmail.com
Yong, et al. Standards Track PAGE 11
RFC TOTAL SIZE: 21280 bytes
PUBLICATION DATE: Thursday, May 8th, 2014
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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