BFD over p2p transport links

Fri Feb 5 16:23:35 UTC 2010

> I'm being asked to look into using BFD over our P2P transport links. Is anyone else doing this? Our transport links are all 10G Ethernet (LAN-PHY). There's no alarming inside of LAN-PHY like there is in SONET. The transport side should propagate a fiber break by stopping to send light on both ends. This is enough to cause the router interfaces to drop and for protocols to converge. 

"The transport side *should* propagate ..." - but are you sure this
will happen in all circumstances? Unless you are certain about this,
you may want BFD.

> Since LAN-PHY doesn't have any built end-end alarming, some folks believe that we may encounter situations where a fiber break doesn't cause interfaces do go down. Convergence would then have to wait for IGP hellos to detect the problem. 
> 
> Is anybody else running BFD over 10G LAN-PHY transport links? Any comments around BFD for this application in general?

We run it on most 10G backbone (LAN-PHY) links.

In addition to the issue of link down propagation, you may also want
to standardize on BFD for all your backbone links, for simplicity's
sake (same mechanism everywhere). Obviously, in order to do this you
want to be sure that the BFD implementation won't give you lots of
false positives.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no