BranoZ_101205
Oct 24, 2008Nimbostratus
interoperability with Per-Vlan RSTP
Hi,
I have LTMs connected to Cisco L2 cloud with mandatory Per-Vlan Rapid STP (PVRST). How should be STP configured on LTMs with minimal impact L2 stability ?
Each LTM is connected with two-link trunk to two Cisco switches (see attached topology). There are multiple VLANs on each trunk. Those Vlan have _different_ L2 topologies. The EtherChannel interface on Cisco is configured as if connected to other switch:
spanning-tree mode rapid-pvst
interface Port-channel2
description ltm02 trunk
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 411,413-415,459
switchport mode trunk
spanning-tree cost 100
end
The problem here is that LTMs don't support PVRST. Currently it is configured for STP (for historical reasons). The problem that happened to me twice in last few months was that the L2 loops were created after major failures (topology changes). Last time the LTM-Cisco trunk was part of the loop and STP stabilized immediately after the trunk was brought down. I'm not completely sure LTM is to blame, but I cannot rule it out either..
Looking at the supported STP modes, "pass-through" looks like the best candidate in case the rest of the network speaks PVRST.
Any recommendations ?