A kernel capabilty which caches the normal round trip time (RTT) between the machine and another host. Route caching is used to optimize how quickly packets are resent to accomodate for lost packets.

Most systems do not use route caching, instead using a defualt (usually 3 seconds) timeout to determine when to resend packets. If a packet is dropped between two machines with a normal RTT of 0.5 seconds, this can add as much as 2.5 seconds of latency per dropped packet.