Packet over SONET failback

Rob Evans internetplumber at gmail.com
Mon Feb 14 05:47:29 CST 2011


> PoS failure detection happens in under 50ms, but what about the failback?  Same deal?  I ask because I've got two routers connected to opposite ends of a spare PoS link that I've been playing with and I'm noticing that the failback on the far side seems to be about 15 seconds (assuming the near side failover was initiated with an interface shutdown command and thusly no shut'd to re-enable the link).

I think there are a couple of issues at play here.  First of all,
SONET/SDH restoration happens at layer 1, whereas it looks like you're
waiting for a router to reroute.  Your reroute times will be tied to
recalculation of IGPs.

Secondly, is this with a Cisco?  Try setting "pos ais-shut" on both
sides.  Unless you do that, the router won't generate and AIS, and it
will take the encapsulation timeout (HDLC, PPP) for the interface on
the other side to go down and signal that to the routing protocols on
top.

Rob




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