Modify ICMP TTL value

Unanswered Question
Jun 26th, 2009

We have an application supplied to us by a vendor that verifies connectivity by firing out an ICMP echo request to the vendors back-end server (via a routed vendor "Extranet" connection). We've observed that the ICMP echo request is sent out with a very low TTL value and some of our sites are more hops away than what the TTL is. Is there a way for me to modify the TTL value of these echo requests... perhaps using route/class-maps?



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Giuseppe Larosa Fri, 06/26/2009 - 05:35

Hello Jeff,

no you cannot increase the TTL on user traffic on routers.

you could pretend to have lower router hops in between if you put this traffic inside a GRE tunnel so that it is the external TTL field to be decremented on the path.

For doing so you need to setup GRE tunnels and on remote sites you need a PBR to put these probes over the tunnel

The better solution is to ask them to fix their client SW to use a greater TTL.

Hope to help


jkloet Fri, 06/26/2009 - 05:48

Yes, we are pushing for a fix. Thanks for your suggestions! Jeff


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