1aq Shortest
Path Bridging, ITU-T protection switching, provider bridge backbone traffic engineering,
and IETF TRILL.
416 Chapter 13
IEEE Project P802.1aq Shortest Path Bridging
This project is in progress. Although nothing can be said for certain until the project
has been completed, the scope and purpose of the project are clear, and a consensus
is emerging among the participants. For one, you can expect that SPB will include a
provision for computing the required spanning trees using a link state protocol such
as IS-IS, instead of using the distance vector technology of the current Spanning Tree
Protocols. This will eliminate the ???counting to infinity??? problem.
Second, you can expect SPB to create a spanning tree for each bridge participating in
the protocol. Normally, this list does not include edge bridges, only ???core??? bridges. This
technique allows the bridges to forward every frame along a tree that will carry it to its
destination along the least-cost path. This will require the use of VLAN IDs to identify
bridges, as well as their current use for identifying VLANs. This makes the technique
unsuitable for 802.1ad Q-in-Q provider bridge networks, because of the reduction in
the number of available VLANs, one of which is required for each customer.
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