Can I introduce BFD on-the-fly?

[Kevin Dorrell]

I have a situation where I have an OSFP adjacency between two SVIs on different switches, through multiple L2 hops of the VLAN. (Don't ask why!)  If one of those hops goes down, it will take an unacceptably long time (the OSPF dead time) before the SVIs realise that the adjacency is down, and re-converge.

I have never used BFD, but can I introduce it on the fly?  What happens in the interval between when I configure it on one SVI and before I configure it on the other?  Will the adjacency go down?  Or is it safe?

Kevin Dorrell

Luxembourg

Edited to correct title ;-)

[Joseph W. Doherty · Accepted solution]

You mean BFD?

I believe its "safe" because I recall both sides actively need to use it before its loss will take an IGP down.  I.e. it has to be "up" first.

PS:

Besides BFD, OSPF fast hellos might be considered too.  You might find hardware that doesn't support BFD but does support OSPF fast hellos.

[Kevin Dorrell]

Yes, I mean BFD.  (I couldn't remember if it was "Bi Directional Forwarding" or "Bidirectional Forwarding Detection".

The hardware is Nexus 7700, so I should be OK.

Thanks for your help.

Kevin