JNCIS-SP: IP tunneling.Communications channel between two different networks.
- have traffic traverse the Internet.
- make link redundant.
- hide traffic from firewall.
GRE: Generic Routing Encapsulation.
A GRE header and an outer IP header are added to the packet, adding 24-bytes of overhead. Inner packet is not modified except TTL-1.
GRE uses IP protocol 47 (RFC 1702).
Encapsulates an IP-packet in an IP-packet, adding 20-bytes of overhead. Only IP traffic is allowed (RFC 2003).
Routing requirements for tunnels;
1. tunnel endpoints must have a valid route to the remote endpoint.
2. intermediary devices must have a route towards tunnel endpoint.
By default, tunnels are stateless. Use a keepalive or BFP.
It is recommended to install static routes on tunnel endpoints towards tunnel endpoints to avoid problems with recursive routing.