2. Multiple Spanning Trees Shyam Kaluve ( skaluve@cisco.com ) IEEE 802.1s 05/21/2001 St. Louis Interim

3. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve2 Common Spanning Tree (Now) Root

4. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve3 Common Spanning Tree (802.1s)

5. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve4 Typical Deployment A standalone 802.1s network Old SST bridges in access layer CST root in MST backbone MSTs must not be affected by CST

6. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve5 MST Super Bridge

7. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve6 Single Bridge vs Super Bridge Switch fabric - MST instances Fabric structure is internal to the bridge - MST structure must be internal Fabric operation independent of CST - So should be MST operation Sync/ReRoot are atomic - Should propagate a cut in all MSTs Bridge ID,Message Age are different

8. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve7 R Single Bridge vs Super Bridge Path Costs are not accurate

9. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve8 R Single Bridge vs Super Bridge ABC Designated Bridge ID does not matter Y Z X

10. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve9 MST Region Transitive closure of MST bridges Either this MST Bridge is the only member of the MST Region Or this MST bridge is interconnected by an internal LAN to one or more MST bridges having the same Region Config

11. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve10 Internal LAN LAN L is internal to a bridge B if the designated bridge D for L also has the same Region Configuration as B Thanks to Mick

12. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve11 MST Region R

13. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve12 ISTP Holds Super Bridge together Distributes CST info Conveys MST Region Config Identifies boundaries Conveys Sync/ReRoot of Super Bridge

14. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve13 Super Sync

15. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve14 Super Sync All MST ports are forcefully blocked Till agreement on IST Master is reached Request for Super Sync is propagated to downstream bridges in IST May result in partial Super Sync that reverses direction

16. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve15 Partial Super Sync

17. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve16 MSTP Current 7 component priority vector Alters M-trees unnecessarily Results in instability every time CST priority changes Convergence follows CST convergence Either requires more space or propagates inconsistent CST info

18. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve17 MSTP Regular 4 component priority vector is sufficient Operates the Super Bridges internal switch fabric Totally unaffected by CST changes in a single 802.1s cloud

19. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve18 Boundary Ports IST port state overrides M-ports All M-ports are edge ports IST Root/Designated MST Designated IST Alternate MST Overridden IST Backup MST Designated/Alternate IST+MST CST

20. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve19 Rapid Transition If IST port is root port and becomes forwarding At the boundary Or if IST port is Designated and gets an agreement - then set agreement for all M-ports

21. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve20 ISTP {C-Root, C-Cost, C-Bridge, C-Port, I-Master, I-Cost, I-Bridge, I-Port} Include CST Designated Bridge and Port ID to make an 8 component vector Introduce IST Flags to indicate SuperSyncRequest

22. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve21 Independence From CST MST instances can use totally different algorithm Separate hello-timer, forward-delay, max-age within the region (?) Change in Super Bridges root port does not necessarily cause a Super Sync

23. 05/21/2001IEEE 802.1s - St. Louis Interim - Shyam Kaluve22 Conclusion ISTP makes the Super Bridge –Identifies boundaries –Overrides MST ports at boundary –Triggers and Propagates Super Sync –May optionally carry some VLANs –Carries Region-Config and M-records MSTP is a much simplified 802.1w

24. Multiple Spanning Trees Shyam Kaluve ( skaluve@cisco.com ) IEEE 802.1s 05/21/2001 St. Louis Interim