Why DMVPN not worked when GRE tunnel coexist?

[zexinfinite]

Hi all,

I got the issue when DMVPN and GRE tunnel coexist, then NHRP will have issue.

For some reason, I need to create GRE tunnel over IPsec first, then I need to migrate to DMVPN with same IPsec configuration.

After I enable DMVPN, then I can not reach the tunnel IP via NHRP, but the other sites which only have DMVPN without the issue.

May I know the reason why DMVPN and GRE tunnel can not coexist between same source and destination? Is that cause by IPsec behavior?

[Karsten Iwen]

The router does not know which tunnel a received packet belongs to. I've never tested it in the combination GRE/DMVPN but I assume it will work when you add tunnel-keys to your interfaces.

[MHM Cisco World]

DMVPN tunnel destination more are multipoint <-need NHRP to get tunnel destination 

GRE tunnel destination<- no need NHRP