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BranoZ_101205's avatar
BranoZ_101205
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Oct 24, 2008

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 ?

 

config
design

3 Replies

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  • John_Heyer_4582's avatar
    John_Heyer_4582
    Icon for Nimbostratus rankNimbostratus
    Nov 11, 2009
    According to Cisco, RPVST should be backwards compatible with RSTP. However, when I try to set STP on the LTM, it just acts as a transparent bridge. It never sees the STP root (which is directly attached) and never puts any ports in blocking state. Instead, that is done by one of the Cisco switches.

     

     

    I'd be curious how things would work with MSTP....

     

  • jason_57094's avatar
    jason_57094
    Icon for Nimbostratus rankNimbostratus
    Dec 08, 2009
    I get the same outcome. I have a similar situation with 2 F5's and 2 Cisco 6513's running rapid-pvst and no matter what I try, the F5's don't see the other switches, always put all their links in forwarding state ( designated ) and think they are the root bridge.