802.1s Multiple Spanning Tree Flavours

Hello group,

Anyone knows the keys differences between the Cisco MST pre-standard
implementation and the Cisco MST standard compliant feature ?

I just found that a Cisco 2940 running 121-22.EA13 and a Cisco 3550 running
122-44.SE6, run these two different versions of MST.

I have a triangle, the 2940 connects to two 3550's like this:

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**********
ws-c2940#sh cdp neighbors
Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge
                  S - Switch, H - Host, I - IGMP, r - Repeater, P - Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID
ws-c3550-1 Fas 0/1 160 R S I WS-C3550-2Fas 0/24
ws-c3550-2 Fas 0/2 128 R S I WS-C3550-2Fas 0/24
ws-c2940#
****************************************************************************
**********

The 3550's interconnect via the Gig0/2 interfaces.

What I see on the 3550's:

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ws-c3550-1#sh spanning-tree mst 0

##### MST0 vlans mapped: 2-9,11-19,21-29,31-99,103-4094
Bridge address 0009.e8cb.6280 priority 32768 (32768 sysid 0)
Root this switch for the CIST
Operational hello time 2 , forward delay 15, max age 20, txholdcount 6
Configured hello time 2 , forward delay 15, max age 20, max hops 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/24 Desg FWD 200000 128.24 P2p Bound(STP)
Gi0/2 Desg FWD 20000 128.26 P2p

****************************************************************************
**********
ws-c3550-2#sh spanning-tree mst 0

##### MST0 vlans mapped: 2-9,11-19,21-29,31-99,103-4094
Bridge address 0011.926c.bb80 priority 32768 (32768 sysid 0)
Root address 0009.e8cb.6280 priority 32768 (32768 sysid 0)
              port Gi0/2 path cost 0
Regional Root address 0009.e8cb.6280 priority 32768 (32768 sysid 0)
                                      internal cost 20000 rem hops 19
Operational hello time 2 , forward delay 15, max age 20, txholdcount 6
Configured hello time 2 , forward delay 15, max age 20, max hops 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/24 Desg FWD 200000 128.24 P2p
Gi0/2 Root FWD 20000 128.26 P2p

ws-c3550-2#
****************************************************************************
**********

What I see on the 2940:

****************************************************************************
**********
ws-c2940#sh spanning-tree mst 0

###### MST00 vlans mapped: 2-9,11-19,21-29,31-99,103-4094
Bridge address 001b.2a66.38c0 priority 32768 (32768 sysid 0)
Root address 0009.e8cb.6280 priority 32768 (32768 sysid 0)
            port Fa0/1 path cost 200000
IST master this switch
Operational hello time 2, forward delay 15, max age 20
Configured hello time 2, forward delay 15, max age 20, max hops 20

Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/1 Root FWD 200000 128.1 P2p Bound(PVST)
Fa0/2 Altn BLK 200000 128.2 P2p Bound(PVST)

ws-c2940#
****************************************************************************
**********

The 3550-1 says:
Bridge address 0009.e8cb.6280
Root this switch for the CIST
Fa0/24 Desg FWD 200000 128.24 P2p Bound(STP)

The 3550-2 agrees on that:
Root address 0009.e8cb.6280
Regional Root address 0009.e8cb.6280
Fa0/24 Desg FWD 200000 128.24

The 2940 says:
Bridge address 001b.2a66.38c0
Root address 0009.e8cb.6280
IST master this switch
Fa0/1 Root FWD 200000 128.1 P2p Bound(PVST)
Fa0/2 Altn BLK 200000 128.2 P2p Bound(PVST)

The 3550-1 says it is the CIST regional root, the 2940 says it is the IST
master.

Thanks.

Regards,

Antonio Soares, CCIE #18473 (RS/SP)
amsoares_at_netcabo.pt
http://www.ccie18473.net

Blogs and organic groups at http://www.ccie.net
Received on Wed Feb 12 2014 - 11:49:58 ART