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New Member

CAT 6509 STP compatibility issues with F5 LTM

Hello all,

We have connected a single F5 box with dual links to 2 different Cisco Catalyst switches using 802.1Q trunks. F5 is configured with RSTP mode and on Cisco Switch RPVST+ is configured.

STP root bridge is hardcoded on the Cisco side. Loop Guard is globally enabled.

On F5 STP link type is Auto, STP Edge port is disabled since that port is connected to the cisco switch.

When we are failing over the F5 primary link to the secondary link we see 'Loop Inconsistent' on the cisco switch and things dont work after the failover.

We have tried configuring the F5 as STP passthrough but that doesn't fix out the issue.

I have checked out the forums and found out following recommendations

1. Configuring MSTP bw F5 and Cisco for better compatibility (Not possible from Cisco side because of a major change in large production setup)

2. Configuring VSS in Cisco switches (not possible due to hardware limitation)

3. Connecting F5 using single links to each switch (redundancy compromised)

I am wondering that on which default vlan does the F5 STP instance0 sends the STP BPDUs ? the term used on Cisco side is native vlan and others use PVIDs; that F5 default vlan should match the native vlan on cisco trunk side.

We are surely planning for STP debugging very soon to sort this out.


Everyone's tags (1)
VIP Super Bronze

CAT 6509 STP compatibility issues with F5 LTM

I am not sure if your setup will work.  If you are connecting one F5 to 2 different switches, the switches need to be in VSS mode, if not Etherchannel will not work. I am assuming you are using Etherchannel with LACP.

New Member

CAT 6509 STP compatibility issues with F5 LTM

Both links are not etherchannel but configured as trunks/tagging. F5 boxes can also run STP to avoid loops and participate as switches.