In RIP, when would you enable auto-summary versus manual subnet-specific updates?

• A. Auto-summary on discontiguous networks; manual on simple contiguous networks.
• B. Auto-summary is never used; manual updates are always preferred.
• C. Manual subnet-specific updates are always default; auto-summary is for testing only.
• D. Auto-summary on simple, contiguous networks; manual/subnet-specific on discontiguous networks or where precise subnet info is required.

Answer: (D)

In RIP, auto-summary affects how routes are advertised when crossing major network boundaries. It lets the router summarize subnets to the classful major network, which reduces routing table size. This works well in a simple, contiguous network where all subnets fall under the same major network, so the summary doesn’t hide needed details and routing stays straightforward.

But in discontiguous networks—where parts of the same major network are separated by other major networks—the classful summary can mislead or hide the real subnet topology. In those cases you want precise, subnet-specific updates so each exact subnet is advertised and chosen correctly, avoiding potential reachability issues.

So the best practice is to enable auto-summary on simple, contiguous networks, and use manual, subnet-specific updates on discontiguous networks or when exact subnet information is required.