GRE Tunnel and Natting

[g.berrido]

Dear All

I have a simple set up with a hup GRE/NHRP and a spoke. the spoke has 2 WAN interfaces, f0/0 has a public IP and the GRE tunnel works fine.

The spoke f0/1 gets a private IP from a non cisco VDSL router/modem. On that side the GRE tunnel will not come up. I assume it is because of the NAT/PAT on the VDSL device. I can not figure out what is exacly going on, and what can be done, as I have no control/access over that device..

Thanks ofr your inputs

Best Regards

gb

[Calin C.]

Hello,

Maybe it's just me, but I cannot reconstruct your topology in my head

Do you have a drawing with your topology, or can you make just a basic one and share it with us?

Thanks,

Calin

[g.berrido]

just one hub and one spoke linked by GRE/NHRP. on he spoke I can test the tunnel on either an interface with a public IP or an interface with a private IP behind a VDSl box. The second option does not work.

[paolo bevilacqua]

Generally speaking, GRe cannot work behing third-party NAT.

As a workaround, you can congirue GRE over IPsec, that generally work fine with third-party NAT.

[g.berrido]

It 's also my feeling, I guess it has something to do with NHRP resolution but

I would like to understand the details.