Why is MD5 authentication used in RIP updates, and how does it work at a high level?

• A. To encrypt all routing information for privacy across the network.
• B. To authenticate routing updates and prevent spoofed routes; uses a shared key to generate a hash included with updates.
• C. To compress updates to reduce bandwidth usage.
• D. To randomize timers to avoid synchronization.

Answer: (B)

MD5 authentication in RIP is about ensuring routing updates come from a trusted source and haven’t been tampered with. Routers that share a secret key put a hash value—generated with that key and the update data—into the update. The receiving router, configured with the same key, re-computes the hash and checks it against the one in the message. If they match, the update is accepted; if not, it’s rejected. This prevents someone from injecting fake or altered routes, which could mislead the network.

It’s not about hiding the content of the updates (it doesn’t encrypt routing information), nor about shrinking bandwidth (it doesn’t compress data), nor about changing timers. The key idea is authentication and integrity: only devices with the shared key can produce a valid update, and any tampering will break the hash.