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Community Member

MSTP blocks OSPF !!!

I implement mstp on the core switche (catalyst 4506). When the topology change for the construction of the tree, OSPF is blocking during 1 to 4 seconds, here the error:

Apr 11 13:41:05 CEST: %OSPF-5-ADJCHG: Process 1, Nbr X.X.X.X on VlanX from FULL to DOWN, Neighbor Down: Interface down or detached. So, we lose some information of the tables of routing.

I didn't find any information on this subject on the site, somebody have infos? thank you by advance

3 REPLIES

Re: MSTP blocks OSPF !!!

Hello,

can you post the configs of two OSPF neighbors where this problem is occuring ? This only happens with MSTP, meaning STP does not cause OSPF to be blocked ?

Regards,

GNT

Re: MSTP blocks OSPF !!!

Sorry if I did not understand exactly. Is the problem that you are losing the connection temporarily or permanently?

When you change the STP mode, all ports revert to blocking and you are restarting STP from scratch. This will definitely explain a temporarily loss of connectivity (that can be longer than 4 seconds btw). If you have a permanent issue, then there is probably something else going on. If this is the case, please give additional details on the environment (are there other switches, what STP mode are they in, etc...).

Regards,

Francois

Community Member

Re: MSTP blocks OSPF !!!

We implemented MSTP on one router (SR1) and two switches (S1, S2), they are connected like folowing:

SR1

Gi 1/1 Gi 3/5

| |

Gi 1/0/24 Gi 0/1

S3 S2

Gi 1/0/23

|

Fa 0/24

Configuration mstp SR1:

#spanning-tree mode mst

#spanning-tree mst configuration

#name coeur

#revision 1

#end

#conf t

#spanning-tree mst 0 root primary

Configuration mstp S1:

#spanning-tree mode mst

#spanning-tree mst configuration

#name coeur

#revision 1

#end

Configuration mstp S2:

#spanning-tree mode mst

#spanning-tree mst configuration

#name coeur

#revision 1

#end

#conf t

#spanning-tree mst 0 root secondary

OSPF: This equipements are configured on area 0.

When the topology changes, the interface of the router becomes down during 23 seconds and we lose the tables of routing. I think is due at the transition of the port SFP, when the port passed of the state "blocked" during the recalculation of stp?

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