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STA and Reconfigurations

STA and Reconfigurations. Network Protocols and Standards Autumn 2004-2005. Designated Bridge. If a bridge receives better BPDU on a port than the one it would transmit, it will no longer transmit BPDUs on that port

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STA and Reconfigurations

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  1. STA and Reconfigurations Network Protocols and Standards Autumn 2004-2005 CS573: Network Protocols and Standards

  2. Designated Bridge • If a bridge receives better BPDU on a port than the one it would transmit, it will no longer transmit BPDUs on that port • As a result, only one bridge called the “designated bridge” transmits configuration BPDUs on each LAN CS573: Network Protocols and Standards

  3. Root ID and Cost: determining • Consider B with bridge ID 18 • Best BPDUs on each of its ports are: <RootID>.<Cost>.<TransmitterID> • Port 1 <12>.<93>.<51> • Port 2 <12>.<85>.<47> • Port 3 <81>.<0>.<81> • Port 4 <15>.<31>.<27> • Root bridge ID is determined as 12 • Least cost is determined as 85+1 = 86 • Port 2 is regarded as the Root port …cont… CS573: Network Protocols and Standards

  4. Root ID and Cost: determining • At next opportunity, B will transmit • <12>.<86>.<18> • Better than the best BPDUs on all ports • Ports 1, 3, and 4 are designated • B considers itself designated for those three segments • B continues transmitting BPDUs on those segments (through respective ports) CS573: Network Protocols and Standards

  5. Spanning Tree Ports • For each bridge, what ports are “included” in the spanning tree? • Root Port • On which best of the best BPDUs is received • Designated Port • Connected to segments on which B is designated • Ports selected in the spanning tree are placed in the forwarding state • B will forward data packets to and from those ports CS573: Network Protocols and Standards

  6. Ports Blocked • Bridge B will block a port if it receives a better BPDU on that port than the one it would transmit (except for the root port) • Bridge B will no longer transmit BPDUs on either root port or blocked ports • Data packets are not forwarded to and received from the blocked ports CS573: Network Protocols and Standards

  7. Port 1 Bridge ID 92 Port 5 Port 4 Port 2 Port 3 41.13.90 81.0.81 41.12.111 41.12.315 41.19.125 Example Root Bridge is selected as 41 Least cost to root is 12+1 = 13  Port 4 is selected as root Now B92 will transmit a BPDU 41.13.92 What does it do with the ports? CS573: Network Protocols and Standards

  8. How the Ports are treated? Remember: B92 will transmit a BPDU 41.13.92 • Port 1: 41.13.92 < 81.0.81  DP • Port 2: 41.13.92 < 41.19.125  DP • Port 3: 41.13.92 > 41.12.315  BP • Port 4: 41.13.92  Root Port • Port 5: 41.13.92 > 41.13.90  BP CS573: Network Protocols and Standards

  9. Example Port 1 Bridge ID 92 Port 5 Port 4 Port 2 Port 3 41.13.90 81.0.81 41.12.111 41.12.315 41.19.125 Blocked Port Designated Bridge on this port Designated Bridge on this port Blocked Port Root Port Bridge B92 becomes designated on Ports 1 and 2 It overwrites messages on those two ports CS573: Network Protocols and Standards

  10. Example Port 1 Bridge ID 92 Port 5 Port 4 Port 2 Port 3 41.13.90 81.0.81 41.12.111 41.12.315 41.19.125 What if B92 were actually B15 with a bridge ID 15? CS573: Network Protocols and Standards

  11. Sample Topology – step 1 DP (1.0.1) 1 DP (1.0.1) DP (4.0.4) DP (5.0.5) DP (7.0.7) 4 5 7 DP (4.0.4) DP (5.0.5) DP (7.0.7) DP (8.0.8) DP (6.0.6) DP (10.0.10) 8 6 10 DP (8.0.8) DP (6.0.6) DP (10.0.10) DP (11.0.11) DP (2.0.2) 11 2 DP (11.0.11) DP (2.0.2) DP (0.0.0) DP: Designated Port 0 DP (0.0.0) CS573: Network Protocols and Standards

  12. Sample Topology – step 2 DP (1.0.1) 1 DP (1.0.1) RP RP RP 4 5 7 DP (1.1.4) DP (1.1.5) DP (1.1.7) RP DP (2.1.6) DP (2.1.10) 8 6 10 DP (4.1.8) RP RP DP (0.1.11) DP (0.1.2) 11 2 RP RP DP (0.0.0) RP: Root Port DP: Designated Port 0 DP (0.0.0) CS573: Network Protocols and Standards

  13. Sample Topology – step 3 DP (1.0.1) 1 DP (1.0.1) RP RP RP 4 5 7 DP (1.1.4) DP (1.1.5) BP RP DP (0.2.6) DP (0.2.10) 8 6 10 DP (1.2.8) RP RP BP DP (0.1.2) 11 2 RP RP RP: Root Port DP: Designated Port BP: Blocked Port DP (0.0.0) 0 DP (0.0.0) CS573: Network Protocols and Standards

  14. Sample Topology – step 4 DP (1.0.1) 1 DP (1.0.1) DP (0.3.4) DP (0.3.5) DP (0.3.7) 4 5 7 RP RP RP RP DP (0.2.6) DP (0.2.10) 8 6 10 DP (0.3.8) RP RP BP DP (0.1.2) 11 2 RP RP RP: Root Port DP: Designated Port BP: Blocked Port DP (0.0.0) 0 DP (0.0.0) CS573: Network Protocols and Standards

  15. Sample Topology – step 5 DP (0.4.1) 1 RP DP (0.3.4) BP BP 4 5 7 RP RP RP RP DP (0.2.6) DP (0.2.10) 8 6 10 DP (0.3.8) RP RP BP DP (0.1.2) 11 2 RP RP RP: Root Port DP: Designated Port BP: Blocked Port DP (0.0.0) 0 DP (0.0.0) CS573: Network Protocols and Standards

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