icmp redirect
ICMP redirects are messages telling a host to deliver the next packet for the same destination IP address to a different router.
ICMP redirects are used by routers to specify better routing paths out of one network, based on the host choice, so basically it affects the way packets are routed and destinations.
This can happen for two reasons:
- There are two routers in the subnet, the first being the default gateway. The host sends a packet to a remote network which is only reachable through the second router. Instead of sending it to that router the host sends it to its default gateway, which forwards it to the correct (second) router, and tells the client to sent it to that router the next time.
Solution: add static route to host to tell it to use the second router for that specific destination
- The host has a bad subnet mask configured, so when trying to send a packet to a node in the same subnet it sends the packet to the default gateway instead. That happens when the subnet mask is too narrow, forcing the host to think that it cannot reach the target directly.
Solution: fix the bad subnet mask setting on the host
Proxy ARP
the technique in which one host, usually a router, answersARPrequests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination.
First Hop Redundancy protocols
will allow default gateway redundancy, meaning, having more than one default gateway enabled, in the event of a router failure there’s a backup device that will kick in and almost transparently to users, continue to forward traffic to remote networks
HSRP (Hot Standby Routing Protocol)