Technical Summary
The TRILL protocol provides optimal pair-wise forwarding without
configuration, safe forwarding even during periods of temporary
loops, and support for multipathing of both unicast and multicast
traffic. It achieves these goals using IS-IS routing and
encapsulation of traffic with a header that includes a hop
count. Devices implementing TRILL are called RBridges or Routing
Bridges.
RBridges are compatible with previous IEEE 802.1 customer bridges as
well as IPv4 and IPv6 routers and end nodes. They are as invisible to
current IP routers as bridges are and, like routers, they terminate
the bridge spanning tree protocol. As customer devices, RBridges do
not supply provider or provider backbone bridging services but
provider or provider backbone bridges may be used to interconnect parts
of an RBridge campus.
The design supports customer VLANs and optimization of the
distribution of multi-destination frames based on VLAN and IP
derived multicast groups. It also allows unicast forwarding tables
at transit RBridges to be sized according to the number of RBridges
(rather than the number of end nodes), which allows these
forwarding tables to be substantially smaller than in conventional
customer bridges.
Working Group Summary
The working group process included two working group last calls (an
MTU problem was discovered by an implementor after the first WG
last call thus a second last call was done to make sure the MTU
changes had sufficient review) as well as the usual review by
working group members. In addition, the working group charter
required special reviews by IEEE 802.1 and two reviews by
independent IETF experts. As the combined result of all of these
steps, the document received an unusually thorough review.
Document Quality
The document is high quality due to the unusually thorough reviews
it has been subject to. An earlier version was implemented by Sun
Microsystems and the lessons learned were incorporated. Independent
IETF experts Dan Romascanu and Bernard Aboba did particularly
thorough reviews and their comments were resolved. Several
implementations are underway although not publicly announced.
Personnel
Erik Nordmark (erik.nordmark@sun.com) is the Document Shepherd. Ralph
Droms is the responsible AD.