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December 2007TRILL WG Vancouver1 TRILL issue: Pseudonodes Radia Perlman

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Presentation on theme: "December 2007TRILL WG Vancouver1 TRILL issue: Pseudonodes Radia Perlman"— Presentation transcript:

1 December 2007TRILL WG Vancouver1 TRILL issue: Pseudonodes Radia Perlman

2 December 2007TRILL WG Vancouver2 What’s a pseudonode? It’s an IS-IS concept for efficiency Originally there were just pt-to-pt links Along came Ethernet –Overhead of routing algorithm proportional to # of links –If there were a fully connected LAN with n routers, that’s n 2 links

3 December 2007TRILL WG Vancouver3

4 December 2007TRILL WG Vancouver4 How a pseudonode works One router is appointed “Designated Router” That router gives a 7-byte name to the LAN Each router has a 6-byte “system ID” A router’s “name” is system ID | “0” Pseudonode name is, typically, DR’s system ID | number assigned by DR

5 December 2007TRILL WG Vancouver5 R1 R2 R7 R6 R5 R3 R4 R1 R2 R7 R6 R5 R3 R4 Without pseudonode With pseudonode R1 names LAN “R1.25” R1: nbrs R2, R3, R4, R5, R6, R7 R2: nbrs R1, R3, R4, R5, R6, R7 R3: nbrs R1, R2, R4, R5, R6, R7 R4: nbrs R1, R2, R3, R5, R6, R7 R5: nbrs R1, R2, R3, R4, R6, R7 R6: nbrs R1, R2, R3, R4, R5, R7 R1.25: nbrs R1, R2, R3, R4, R5, R6, R7 R1: nbr R1.25 R2: nbr R1.25 R3: nbr R1.25 R4: nbr R1.25 R5: nbr R1.25 R6: nbr R1.25 R7: nbr R1.25

6 December 2007TRILL WG Vancouver6 LSPs Without pseudonode, each router reports each other router on the link as a neighbor With pseudonode, each router on the link reports one neighbor (the pseudonode), and the Designated Router additionally issues and LSP claiming to be the pseudonode, listing the n routers on the link

7 December 2007TRILL WG Vancouver7 But not all “Ethernets” are huge LANs With RBridges, most ports will be pt-to-pt If every port were a pseudonode, even those to endnodes, that would be ridiculous 2 RBridges on a link: –With pseudonode, 3 LSPs –Without, 2 LSPs

8 December 2007TRILL WG Vancouver8 Overhead with n RBridges N RBridges –With pseudonode: n+1 LSPs, 1 link reported in n LSPs, n links reported in 1 LSP –Without pseudonode: n LSPs, each with n-1 links reported

9 December 2007TRILL WG Vancouver9 We’d like to do something sensible Don’t have pseudonodes if “very few” RBridges on the link Do have pseudonodes if “a lot” of RBridges on the link Don’t have configuration Don’t have disruption if RBridges go up and down

10 December 2007TRILL WG Vancouver10 Claim With only endnodes on a link, really don’t want pseudonode With “few” RBridges, preferable to not have pseudonode With “a lot” of RBridges, much better to have pseudonode Large grey area between “few” and “a lot” where it’s OK with or without pseudonode

11 December 2007TRILL WG Vancouver11 Observation It would be bad if different RBs on the link simultaneously made different decisions re pseudonode or not But we have one RB, the DRB, that can dictate to the rest There does not have to be a single agreed-upon algorithm for how the DRB decides However, it’s nice to have a recommendation

12 December 2007TRILL WG Vancouver12 Recommendation in the spec If DRB has one or zero RBridge neighbors, no pseudonode If DRB has 4 or more RBridge neigbors, use pseudonode If DRB has 2 or 3 RBridge neighbors, keep state the same

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