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Is rtr-2-rtr gre tunnel a TCP connection?

I have a bunch of IP packets (UDP, ICMP, TCP, SNMP) that I am planning on tunneling from one endpoint to another using a GRE tunnel. Challenge is the tunnel is going to go though a router that only allows TCP traffic, and does check the TCP Established bit on the return.

So, I need to confirm if a GRE tunnel runs over TCP, and would be nice to also know if that checking of the established bit is going to cause me headaches.

Surfed quite a bit on CCO and did not see the data I'm looking for on GRE. If anybody has any thoughts, or knows of any links with the data, I would greatly appreciate it!

Thanks.

1 REPLY
Cisco Employee

Re: Is rtr-2-rtr gre tunnel a TCP connection?

GRE is its own protocol that sits right on top of IP, just like UDP and TCP do. It is NOT TCP based. It uses IP protocol number 47. If this router only allows TCP then you're going to run into trouble with GRE. If you need to add an access-list into it, you would do it like:

access-list 100 permit gre

Hope that helps.

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