Route authentication allows routers to authenticate routing updates by exchanging passwords or keys. It prevents routers without the correct authentication from participating in the routing process. There are two main types: simple password authentication uses a shared password, while MD5 authentication uses cryptographic hashes to authenticate packets without sending the key over the wire, making it more secure. The document provides sample configurations for enabling simple password authentication on RIPv2, EIGRP and OSPF routing protocols. It also explains how to configure MD5 authentication which involves additional commands to change the authentication mode.