From: Bit Gossip (bit.gossip@chello.nl)
Date: Sun Apr 08 2007 - 12:46:54 ART
Hi group,
I have noticed that in the following topology S4 detects a loop and put
f1/0/21 in BLK state with a role of back-up interface.
All the interfaces are in vlan 1363; STP is disabled for vlan 1363 on S3.
Rack1SW4#show spanning-tree vlan 1363
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa1/0/20 Desg FWD 19 128.22 P2p
Fa1/0/21 Back BLK 19 128.23 P2p
S3 f0/20 ---------------------- S4 f0/20
S3 f0/21 ---------------------- S4 f0/21
I struggle to understand how S4 can detect the loop; I think the only possible
explanation is:
Once STP is disabled on a certain interface, SW3 doesn't absorb the BPDU from
SW4 anymore; instead it floods them out all ports of the same vlan.
SW4 at this point can hear on f0/21 its own BPDU that it sent out of f0/20; so
it detects the loop and put f0/21 in BLK state with a back-up role.
Is my guess correct?
Thanks,
Luca.
PS: no need for flex-link then :-)
This archive was generated by hypermail 2.1.4 : Tue May 01 2007 - 08:28:35 ART