Performance of the rapid spanning tree protocol in ... - RuggedCom

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T L + (n-2+1+1)*T PA S n-1… {S n-2 ,…,S 3 }T L + (n-2+1+1)*T PA + (n-3)*T PA S 2T L + (n-2+1+1)*T PA + (n-3)*T PA+ T PAS nS 1S 2… {S 3 ,…,S -2 }S n receives proposal BPDUs from S n-1 and S -(n-1)at virtually the same time. For the worst casescenario, we assume that the proposal from S n-1is received and processed first (as you will seebelow, this case causes certain network“confusion” and thus requires more RSTPactions to resolve it).Since S n doesn’t have any information about theS 0 failure yet, it will change its old AlternatePort role to Root Port and “reject” the S n-1 ’sproposal by sending its own proposal with betterbut actually obsolete information about S 0 . Thisinfo will “confuse” all { S n-1 ,…,S 1 } switches.Right after that, S n will process S -(n-1) ’s proposalabout S -1 as Root. As S n receives that proposalfrom its only path to the Root, it immediatelyages out the old Root information and startsProposal-Agreement handshaking with S n-1again – this time proposing S -1 as Root. The newProposal is now fixing the “confusion” justcaused by the previous Proposal about S 0 .S n-1 starts Proposal-Agreement handshakingwith S n-2 about S -1 as Root.The Proposal-Agreement handshaking occurs oneach hop back to S 2 .All switches in the ring except S 1 erroneouslyagree about S -1 being Root. S 2 sends Proposal toS 1 about S -1 as Root.Being a better Root candidate, S 1 responds withits own Proposal about itself as Root.Final round of handshaking starts from S 2towards S -1 – this time for the real best Rootcandidate S 1 .The Proposal-Agreement handshaking occurs oneach hop all the way to S -1 .Figure 13Figure 14--Figure 15Figure 16--12
T L + (n-2+1+1)*T PA + (n-3)*T PA+ T PA + (2*n-3)*T PAS -1All switches in the network agree about S 1 beingRoot and all ports are in Forwarding state.Connectivity is restored.Figure 17Note that in the analysis Topology Change notification was not even mentioned because it propagatesalong with the initial round of handshaking, i.e. much before the final topology is achieved.S 0S 0S -1S -2S 1. . . . . .S -(n-2)S (n-2)S -(n-1)S 2S (n-1)S nS -1S -2S 1. . . . . .S -(n-2)S (n-2)S -(n-1)Root=S-1S 2S (n-1)S nRoot=S1Figure 11.S 1 and S -1 declare themselves as RootFigure 12.{S 1 ,…,S n-1 } agree about S 1 , while{S -1 ,…,S -(n-1) } agree about S -1S 0S 0S -1S -2S 1. . . . . .S -(n-2)S (n-2)S -(n-1)S 2S (n-1)S nFigure 13.Root=S0S -1S -2S 1. . . . . .S -(n-2)S (n-2)S -(n-1)Root=S- 1S 2S (n-1)S nFigure 14.Root=S-1 Root=S0Root=S0S n sends obsolete proposal about S 0being Root13S n sends new proposal about S -1being Root
Page 1: Performance of the Rapid Spanning T
Page 4 and 5: 2.2.3 Enhanced RSTP (eRSTP TM )Alth
Page 6 and 7: 3.1 Symbols and AssumptionsThe symb
Page 8 and 9: Table 1. Time-line of RSTP actions
Page 10 and 11: Traffic sourceTraffic destinationS
Page 14 and 15: S 0S 0S -1S -2S 1. . . . . .S -(n-2
Page 16 and 17: 4. Extrapolation to Meshed Networks
Page 18 and 19: 5. Empirical Performance DataTo cor
Page 20 and 21: ProtocolVendorCan be used inmulti-v
Page 22: 9. BiographiesMichael Pustylnik is

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