Alternatives for Multilevel TRILL (Transparent Interconnection of Lots of Links)

Document Type Replaced Internet-Draft (trill WG)
Last updated 2015-10-14 (latest revision 2015-07-05)
Replaced by draft-ietf-trill-rbridge-multilevel
Stream IETF
Intended RFC status (None)
Expired & archived
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Stream WG state Adopted by a WG
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IESG IESG state Replaced by draft-ietf-trill-rbridge-multilevel
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


Extending TRILL to multiple levels has challenges that are not addressed by the already-existing capability of IS-IS to have multiple levels. One issue is with the handling of multi-destination packet distribution trees. Another issue is with TRILL switch nicknames. There have been two proposed approaches. One approach, which we refer to as the "unique nickname" approach, gives unique nicknames to all the TRILL switches in the multilevel campus, either by having the level-1/level-2 border TRILL switches advertise which nicknames are not available for assignment in the area, or by partitioning the 16-bit nickname into an "area" field and a "nickname inside the area" field. The other approach, which we refer to as the "aggregated nickname" approach, involves hiding the nicknames within areas, allowing nicknames to be reused in different areas, by having the border TRILL switches rewrite the nickname fields when entering or leaving an area. Each of those approaches has advantages and disadvantages. This informational document suggests allowing a choice of approach in each area. This allows the simplicity of the unique nickname approach in installations in which there is no danger of running out of nicknames and allows the complexity of hiding the nicknames in an area to be phased into larger installations on a per- area basis.


Radia Perlman (
Donald Eastlake (
Mingui Zhang (
Anoop Ghanwani (
Hongjun Zhai (

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)