Gre tunneling issue

[arjun_4790]

i was trying to create gre tunnel..but couldn't do it..i'm gonna attach a screenshot of  a tunnel output..could anyone resolve my issue

[Giuseppe Larosa]

Hello @arjun_4790 ,

the tunnel source address is Unknown .

Being the device a switch you have probably configured as source interface an OSI layer 2 interface.

You need to use a routed interface or an SVI as source interface.

GRE encapsulation requires to build an external IP header with a valid IP source and a valid IP destination.

Being a switch and depending on platform the GRE tunnel feature may be unsupported. This is another possible explanation for your issue.

Note : you can copy and then past a show version in a text file this is the best way to post configuration and show commands that can be hosted in a txt file.

Hope to help

Giuseppe

[arjun_4790]

thanks sir for replying..its a layer 3 switch..routed interface..given no switchport to the interfaces..and also ipv4 to ipv4 tunnel is working only ipv6 over ipv4 tunnel is not working..no idea sir ..why??

[Giuseppe Larosa]

Hello @arjun_4790 ,

according to your feedback you have issues to use a p2p GRE tunnel to carry IPv6 traffic over IPv4.

This can be a platform limitation as a multilayer switch uses the TCAM to describe possible actions on traffic this form of tunneling may be not supported in hardware = it is not possible to program TCAM for IPv6 traffic so that it is tunneled over IPv4.

You may need to use a SW based router like an ISR to be able to implement a working GRE tunnel to carry IPv6 traffic in the payload.

Tunneling is not a typical feature of multilayer switches, they are very powerful but they have less features when compared to SW based routers.

Hope to help

Giuseppe

[Joseph W. Doherty]

In addition to the points Giuseppe mentioned, if you're new to GRE tunnels, also know, some switches that support GRE might only do some features in software, for example, the sup720 only uses software for IPv6 tunnels. Further, on some devices, a GRE tunnel showing "up" doesn't always mean you have a good end-to-end tunnel.