I need to lock down the outside interface on an 871 router which is currently having a L2L tunnel with a remote router. I need to apply an ACL to the outside interface of this 871 and to allow ONLY the remote router to communicate with my 871 for the purpose of the tunnel. Everything else will be blocked.
Can you tell me what are the exact protocols and port numbers that I need to allow?
It is an IPsec tunnel embedded on a GRE tunnel. The IP address of the remote router is 18.104.22.168