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New Member

question about mstp port status.

topology

switch1-switch2-switch3

first case:

3 switch in same region

switch 1 is root bridge of instance 0,1,2

set switch 1 max-hop of 1

in switch 3:

the port is blocked in instance 0

but forwarding in instance 1 and 2

case2

topology as first

switch 1 is root of instance 0

switch 3 is root of instance 1,2

set switch 3 max-hop 1

in stwich 1:

the port is blocked in instance 1 and 2

>>>>>>>>>

so if case2's result is correct, why the port is forwarding in instance 1 and 2 in case 1?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: question about mstp port status.

Sorry for the late answer. You can file a bug for that. I hoped that the dispute mechanism could have prevented opening the port on the other switch, but it does not happen because they have different CIST Regional Root (aka IST Master).

Actually, I can have someone within Cisco filing a bug on this. If you exceed the max hop within a region, you may end up with a permanent bridging loop because of this (I guess that's what you were testing).

Regards,

Francois

4 REPLIES

Re: question about mstp port status.

Hi!

That's an interesting test. The asymetric behavior looks like a bug to me. It is likely that as soon as the CST information is considered aged, the MSTI information is not processed on switch 3 (case 1), which is incorrect.

In case 1, assuming that you are running the latest software, could you let me know the state of instance 1 and 2 on the port of switch 2 leading to switch 3?

Thanks and regards,

Francois

New Member

Re: question about mstp port status.

hi,Francois

thanks

yes they latest version

cisco1,3 is 3550 -12.2(25)SEE2

cisco2 is 3750 -12.2(25)SEE2

cisco 2 status. all forwarding

Switch(config)#do show sp m

##### MST0 vlans mapped: 1-9,11-19,21-4094

Bridge address 0012.43f8.c880 priority 32768 (32768 sysid 0)

Root address 000b.46c8.2180 priority 32768 (32768 sysid 0)

port Gi1/0/1 path cost 0

Regional Root address 000b.46c8.2180 priority 32768 (32768 sysid 0)

internal cost 200000 rem hops 0

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

---------------- ---- --- --------- -------- --------------------------------

Gi1/0/1 Root FWD 200000 128.1 P2p

Gi1/0/2 Desg FWD 200000 128.2 P2p

##### MST1 vlans mapped: 10

Bridge address 0012.43f8.c880 priority 32769 (32768 sysid 1)

Root address 000b.46c8.2180 priority 32769 (32768 sysid 1)

port Gi1/0/1 cost 200000 rem hops 0

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/0/1 Root FWD 200000 128.1 P2p

Gi1/0/2 Desg FWD 200000 128.2 P2p

##### MST2 vlans mapped: 20

Bridge address 0012.43f8.c880 priority 32770 (32768 sysid 2)

Root address 000b.46c8.2180 priority 32770 (32768 sysid 2)

port Gi1/0/1 cost 200000 rem hops 0

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/0/1 Root FWD 200000 128.1 P2p

Gi1/0/2 Desg FWD 200000 128.2 P2p

cisco3 status

Switch# sho spanning-tree mst

##### MST0 vlans mapped: 1-9,11-19,21-4094

Bridge address 000e.83e7.eb00 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

---------------- ---- --- --------- -------- --------------------------------

Fa0/5 Desg BLK 200000 128.5 P2p

Fa0/15 Desg FWD 200000 128.15 P2p

##### MST1 vlans mapped: 10

Bridge address 000e.83e7.eb00 priority 32769 (32768 sysid 1)

Root this switch for MST1

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/5 Desg FWD 200000 128.5 P2p

Fa0/15 Desg FWD 200000 128.15 P2p

##### MST2 vlans mapped: 20

Bridge address 000e.83e7.eb00 priority 32770 (32768 sysid 2)

Root this switch for MST2

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/5 Desg FWD 200000 128.5 P2p

Fa0/15 Desg FWD 200000 128.15 P2p

Re: question about mstp port status.

Sorry for the late answer. You can file a bug for that. I hoped that the dispute mechanism could have prevented opening the port on the other switch, but it does not happen because they have different CIST Regional Root (aka IST Master).

Actually, I can have someone within Cisco filing a bug on this. If you exceed the max hop within a region, you may end up with a permanent bridging loop because of this (I guess that's what you were testing).

Regards,

Francois

New Member

Re: question about mstp port status.

get it

thanks

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