Re: 802.1s Multiple Spanning Tree Flavours

Interesting scenario as I've never had to work on a similar design.
A quick read on cisco.com says that a region can't span between a stand and
pre-stanard, thus the border condition that you see in your switches.

Some of the differences between the 2 are-

detection of uni-directional links
port role naming
in the standards based MST, a designated port is not defined as boundary
unless it is running in an STP-compatible mode.
in the standards based MST, the CIST regional root bridge ID field is now
inserted where an RSTP or legacy 802.1s switch has the sender switch ID.

I'm sure there are others we could find.

Cheers,
Ron

On Wed, Feb 12, 2014 at 6:49 AM, Antonio Soares <amsoares_at_netcabo.pt> wrote:

> 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:
>
>
> ****************************************************************************
> **********
> 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:
>
>
> ****************************************************************************
> **********
> 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
>
>
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Received on Thu Feb 13 2014 - 17:03:36 ART