I have an odd STP issue with a 5000, 5002 and a 3550 in the following simple configuration:
5000 ----------- 3550
1/1-2 0/1-2
isl trunk isl trunk
100/full 100/full
channel1 port-channel 1
6.3(7) 12.1(9)EA1c
SupIII NFFC
These 2 switches are trunked thorugh a 2 port FEC...
A 5002 is redundantly connected to both the 5000 + 3550 with 2 trunks:
1/1 to 5/1 of the 5000 1/2 to 0/3 of the 3550
trunk isl 100/full trunk isl 100/full
The 5002 is using a SupII with 5.5(16)
The 5000 has been set to be the root bridge
The issue is, that ALL ports are forwarding in the STP configuration on all switches... the Po1 between the 5000 + 3550, the 5/1 + 1/1 between the 5000 + 5002, and 0/3 + 1/2 between the 3550 + 5002. For simplicity, VLAN 1 is the only VLAN being used and STP is enabled for VLAN 1 on all switches.
If I remove the FEC between the 5000 + 3550 and leave 2 redundant trunks, everything runs fine with STP and redundant ports that you would expect to be blocked/forwarding according to priority and costs are functioning as you would expect...
I have searched through numerous reference books that I own and have searched this board + TAC and I get no hints why STP fails when the FEC is configured...
I appreciate any help you can offer me!
Thanks for your time...
