Multilink Reachability Lost - When 1 E1 flaps

Unanswered Question
Feb 13th, 2009


I am facing a peculiar issue in my network where we are having multilinks in many locations. When any one of the E1 in the multilink flaps, the reachability to the remote end of the multilink is lost for say 5 packets and comes back. Due to this OSPF and LDP neighborship over multilink goes down and comes up. This creates a huge impact in our network.

I tried configuring the following things:

1. configured keepalive 1 1 under all the E1 interfaces

2. disable fragmentation under multilink

3. configure no fair-queue under all the E1 and multilink as well

but still the problem persists.

Had anyone observed this problem before and what is the fix for this.

Any help is much appreciated.


Arun Kumar

I have this problem too.
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arun kumar Fri, 02/13/2009 - 11:53

Though i m getting 5 packet drops, OSPF and LDP takes couple to minutes to come up again. Since it is happening frequently (atleast twice a day in any one of the location) our customers are impacted mostly VOIP applications.


Arun Kumar

Paolo Bevilacqua Fri, 02/13/2009 - 12:00

Still not sure what 5 packets drops means, packets are not an unit of time.

Send a log trace taken with msecs.

shivlu jain Fri, 02/13/2009 - 22:24


could you tell whether you are using per packet based or per destination based switching.


shivlu jain

Paolo Bevilacqua Sat, 02/14/2009 - 03:27

shivlu, your question is not applicable to the problem.

The OP has multilink, consequently there is no load sharing at routing level on the circuits.

royalblues Sat, 02/14/2009 - 12:44

If the latency on the circuits is not too high try reducing the keepalive on the multilink interface and check whether it improves your failovers..

The voice being carried on the link that flapped will be lost.. Most of the times it is a silence that is experienced and depends on the user whether he continues to hold on or hangs the call



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