An attacker attaches a rogue router in a network. He wants to redirect traffic to a LAN attached to his router as part of a man-in-the-middle attack. What measure on behalf of the legitimate admin can

Routing protocols such as OSPF, EIGRP, and RIP support MD5 or SHA-based neighbor authentication, ensuring that only routers with valid credentials can participate in route exchanges. A rogue router without the correct authentication key cannot advertise routes to legitimate routers, preventing it from redirecting traffic. This directly neutralizes the attacker's ability to perform a man-in-the-middle attack by inserting fraudulent routing information.

Disabling all routing protocols and relying solely on static routes is operationally impractical in most enterprise networks and does not scale as a general security mitigation.

OSPFv3 alone does not mitigate the attack - authentication must be explicitly configured on the routing protocol regardless of version to prevent rogue router participation.

A rogue router physically attached to the network can advertise routes and redirect traffic without any explicit administrative permission, making this statement technically incorrect.