Section 19: IGP Interior Gateway Protocol Fundamentals

In what order does EIGRP select its Router ID if not manually configured?

Highest IP address on a loopback interface; if none exists, the highest IP address on any other active interface.

How many equal-cost paths will EIGRP load balance across by default?

Up to 4.

What multicast address does RIPv2 use to send updates?

224.0.0.9

What's the key difference between RIPv1 and RIPv2 regarding subnet mask information and VLSM support?

RIPv1 doesn't send subnet mask info in updates, so it doesn't support VLSM. RIPv2 does, and supports VLSM.

Which RIP version supports authentication?

RIPv2 only — RIPv1 does not.

What command shows EIGRP neighbor adjacencies?

show ip eigrp neighbors

Which routing protocols perform automatic summarization to classful boundaries by default, and how do you disable it?

RIP and EIGRP both do — disable with no auto-summary

In router eigrp 20, what does 20 represent, and why does it matter?

The Autonomous System (AS) number — it must match between routers for them to form an EIGRP adjacency.

What does EIGRP stand for?

Enhanced Interior Gateway Routing Protocol.

What's a key restriction of the network command in RIP?

It must reference a classful network — no subnet mask is specified, unlike EIGRP where a wildcard mask can be used.

What does show ip protocols display?

The routing protocol(s) running, interfaces participating, Administrative Distance, and neighbor/routing information sources.

What's the purpose of show ip rip database, and when would you use it?

To check whether a route was received by RIP at all — useful when a RIP neighbor relationship exists but an expected route isn't showing up in the routing table (helps distinguish "never received" from "received but not the best route").

What are "bounded updates" in EIGRP, and why do they matter?

EIGRP only sends topology change updates to routers actually affected by the change, rather than flooding the whole network — making it more efficient/faster-converging than protocols with periodic full updates.

In an EIGRP network command, does the wildcard mask determine what's advertised?

No — the wildcard mask only determines which interfaces EIGRP is enabled on (matching against interface IP). What's actually advertised is the network/mask configured on each matching interface, not the network statement's own mask.

If you add a loopback interface to a router with EIGRP already configured, does it immediately become the new Router ID?

No — EIGRP must be restarted (disable/re-enable, or reboot) to pick up the new loopback as the Router ID.

Does a manually configured EIGRP Router ID need to match an IP address actually configured on the router?

No — it just needs to be in IPv4 address format; it doesn't need to correspond to a real interface (though best practice is to use one that does, for clarity).