From: gladston@br.ibm.com
Date: Mon Feb 21 2005 - 20:59:23 GMT-3
I am facing this situation, related to MSTP on catalyst and IRB on router:
CAT1 is connected to R7 through trunk connection.
Vlan 73 connects R7 to R3 and Vlan 74 connects R7 to R4.
There is only one catalyst, CAT1.
CAT1 is configured to spanning-tree mode mstp.
CAT1 port 0/7 is configured as following:
switchport trunk encap dot
switchport mode trunk
R7 has two subinterfaces: fa0/0.73 and fa0/0.74.
Both interfaces are configured to be part of bridge group 1:
bridge irb
bridge 1 protocol ieee
bridge 1 route ip
!
int bvi 1
ip ad 172.16.100.7
int fa 0/0.73
encap dot 73
bridge-group 1
!
int fa 0/0.74
encap dot 74
bridge-group 1
Bridge-group 1 is in blocking mode for int fa0/0.74 and forwarding mode for int fa 0/0.73.
I was expecting CAT1 revert to 802.1D, as it just receives BPDU 802.1D from R7, but it does not.
If I remove the MSTP configuration from CAT1 everything works as expected.
It seems CAT1 sends the same BPDU through both Vlans over the trunk and receives it back from R7, forming a loop.
If the mode is PVST, no problem.
Any Comments?
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