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Webcast-Catalyst9k
New Member

Is there a way to change packets TTL?

Hi

We have a server shat replays with TTL of 15, there is no way we can change the TTL on the server. Is there any way to do this on the IOS router?

Many thanks

/Daniel Nilsson

7 REPLIES
Hall of Fame Super Silver

Re: Is there a way to change packets TTL?

Hello Daniel,

no you cannot increase TTL on routers.

You can try to setup a GRE tunnel to transport the server's answer near the original sender to avoid TTL to expire in transit

Hope to help

Giuseppe

New Member

Re: Is there a way to change packets TTL?

Hi and thanks for the quick answer.

A GRE tunnel would defenitly solve our problem but it in our environment, it would not scale.

Maby a feature request?

Many thanks

/Daniel Nilsson

Hall of Fame Super Silver

Re: Is there a way to change packets TTL?

Hello Daniel,

it would be wise to ask to server's people to patch their TCP/IP stack to use a greater TTL in icmp echo replies.

I wouldn't want to see this feature on a Cisco Router or of any other vendor it would provide ways to defeat the TTL check and could create problems in forwarding efficencies (packet rewrite the IP header checksum needs to be recomputed )

Hope to help

Giuseppe

Hall of Fame Super Silver

Re: Is there a way to change packets TTL?

Hello Daniel,

another thought:

you could think to use MPLS VPN and to place the servers in VRFs in all sites this is clearly more scalable then using point-to-point GRE tunnels

You then can add a point of contact with the global routing table if needed.

Hope to help

Giuseppe

New Member

Re: Is there a way to change packets TTL?

I see, the only way to fix this problem is to change the servers.

Thanks anyway

/Daniel

Super Bronze

Re: Is there a way to change packets TTL?

re: it would not scale

MGRE?

DMVPN (w/o crypto)?

GETVPN?

New Member

Re: Is there a way to change packets TTL?

I strongly dislike large workarounds in 1000+ sites networks. And yes, it would not scale.

Many thanks

/Daniel Nilsson

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