1. It's not an "attack" - it's a broadcast of
routing information from his router to any others in 192.*.*.* that might be interested in reaching the subnet he controls. If you were cooperating rather than in conflict,
ripd(8) could be utilized to automatically update your routing table.
2. You're already blocking these packets, and without a running routing daemon such as ripd, you would have nothing "listening" to the data anyway.