Cisco Catalyst 6500 VSS / BFD OSPF

[johannes.nielandt]

Hi community,

I'm having a Catalyst 6800 VSS with multiple L3 uplinks to routers.
Each of these links are dedicated L3 without MEC.

Is it recommended to use BFD on these interfaces or not?

Especially what happens if my active Sup fails, does it bring down the BFD sessions during switchover?

Thanks for answer,

Johannes

[Reza Sharifi]

Hi,

If you are running OSPF over the L3 links, usually the fail over is within 2 or 3 seconds.  If your requirement is to have faster fail over than 2 or 3 seconds, than you can adjust the OSPF times or enable BFD. 

Here is good doc on BFD

http://www.cisco.com/en/US/technologies/tk648/tk365/tk480/technologies_white_paper0900aecd80244005.html

HTH

[johannes.nielandt]

Hi,

thank you. My problem is a indirect connection via some provider hardware.
No link-state is propagated to the partner router.

I think I have found an answer  in the meantime:

SSO—BFD

12.2(33)SRE 12.2(33)SXI2 12.2(33)XNE 15.0(1)S 15.1(1)SG

Network deployments that use dual RP routers and switches have a graceful restart mechanism to protect forwarding states across a switchover. This feature enables BFD to maintain sessions in a up state across switchovers.

[Reza Sharifi]

Hi,

Correct. SSO is enabled when you are running VSS or a single chassis with 2 sups.

If you issue "sh redundancy" you should see that SSO is enabled.

HTH

[Rolf Fischer]

Johannes,

Especially what happens if my active Sup fails, does it bring down the BFD sessions during switchover?

Unfortunately I'm not sure how VSS interacts with BFD during a switchover but if I remember correctly it's no longer recommended to use BFD on a VSS.

With respect to routing protocols  its important to keep in mind that SSO doesn't synchronize protocol-specific data structures like the OSPF LSDB.

If your VSS has NSF-aware OSPF-neighbors, you should enable NSF (Non-Stop Forwarding) under the OSPF process(es), otherwise you could use NSR (Non-Stop Routing) if your IOS supports it.

HTH

Rolf

P.S.: The CiscoLive on-demand sessions are a very recommendable source of information, e.g. BRKCRS-3035

[smailmilak]

Hi,

we have two 6513 with Sup2T, running in VSS with Quad Supervisor.

Routing protocol is OSPF with NSR enabled and four neighbors are established.

We would like to run BFD for fast convergence in case of link failure but we are not sure it this is the right approach when VSS is used, and does BFD run in hardware on C6513?