Transparent Interconnection of Lots of Links (TRILL): Problem and Applicability Statement
RFC 5556
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RFC - Informational
(May 2009; Errata)
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2015-10-14
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draft-touch-trill-prob
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RFC 5556 (Informational)
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Mark Townsley
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Network Working Group J. Touch
Request for Comments: 5556 USC/ISI
Category: Informational R. Perlman
Sun
May 2009
Transparent Interconnection of Lots of Links (TRILL):
Problem and Applicability Statement
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) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document.
Abstract
Current IEEE 802.1 LANs use spanning tree protocols that have a
number of challenges. These protocols need to strictly avoid loops,
even temporary ones, during route propagation, because of the lack of
header loop detection support. Routing tends not to take full
advantage of alternate paths, or even non-overlapping pairwise paths
(in the case of spanning trees). This document addresses these
concerns and suggests applying modern network-layer routing protocols
at the link layer. This document assumes that solutions would not
address issues of scalability beyond that of existing IEEE 802.1
bridged links, but that a solution would be backward compatible with
802.1, including hubs, bridges, and their existing plug-and-play
capabilities.
Touch & Perlman Informational [Page 1]
RFC 5556 TRILL: Problem and Applicability May 2009
Table of Contents
1. Introduction ....................................................2
2. The TRILL Problem ...............................................3
2.1. Inefficient Paths ..........................................3
2.2. Multipath Forwarding .......................................5
2.3. Convergence and Safety .....................................6
2.4. Stability of IP Multicast Optimization .....................6
2.5. IEEE 802.1 Bridging Protocols ..............................7
2.6. Problems Not Addressed .....................................8
3. Desired Properties of Solutions to TRILL ........................9
3.1. No Change to Link Capabilities .............................9
3.2. Zero Configuration and Zero Assumption ....................10
3.3. Forwarding Loop Mitigation ................................10
3.4. Spanning Tree Management ..................................11
3.5. Multiple Attachments ......................................11
3.6. VLAN Issues ...............................................11
3.7. Operational Equivalence ...................................12
3.8. Optimizations .............................................12
3.9. Internet Architecture Issues ..............................13
4. Applicability ..................................................13
5. Security Considerations ........................................14
6. Acknowledgments ................................................15
7. Informative References .........................................15
1. Introduction
Conventional Ethernet networks -- known in the Internet as Ethernet
link subnets -- have a number of attractive features, allowing hosts
and routers to relocate within the subnet without requiring
renumbering, and supporting automatic configuration. The basis of
the simplicity of these subnets is the spanning tree, which although
simple and elegant, can have substantial limitations. With spanning
trees, the bandwidth across the subnet is limited because traffic
flows over a subset of links forming a single tree -- or, with the
latest version of the protocol and significant additional
configuration, over a small number of superimposed trees. The oldest
version of the spanning tree protocol can converge slowly when there
are frequent topology changes.
The alternative to an Ethernet link subnet is often a network subnet.
Network subnets can use link-state routing protocols that allow
traffic to traverse least-cost paths rather than being aggregated on
a spanning tree backbone, providing higher aggregate capacity and
more resistance to link failures. Unfortunately, IP -- the dominant
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