Exam Essentials

Understand the scalability limitations of routing protocols. Network convergence can take longer than desired with distance-vector routing protocols because of their update interval. More complex configuration is the only real scalability issue with link-state routing protocols.

Understand how distance-vector routing protocols prevent routing loops. Counting to infinity is used to prevent routing loops by setting the maximum hop count to 15. Split horizon enforces the rule that routing information cannot be sent back to the direction from which it came. Route poisoning, along with triggered updates, prevents a route from propagating by entering a hop count of 16; notification updates will occur once the network is up by triggered updates.

Understand the advantages of hybrid routing protocols. Hybrid routing protocols such as EIGRP support multiple routed protocols: IP, IPX, and AppleTalk. EIGRP and IS-IS allow for equal-cost load balancing, incremental routing updates, and formal relationships, combining the best of distance-vector and link-state routing.

Understand the features and operation of Cisco’s EIGRP. EIGRP uses DUAL for metric calculation and supports multiple routed protocols and classless routing. Hello packets are used to form neighbor relationships with acknowledgment, and topology databases are created and route calculations are made.

Know how to configure EIGRP. EIGRP configuration requires an autonomous system number for all routers in the same domain along with network, bandwidth, passive-interface and distribute-list commands for proper configuration.

Understand the routing protocol types. RIP, IGRP, and RTMP are distance-vector routing protocols. EIGRP and IS-IS are hybrid protocols, and OSPF and NLSP are link-state protocols.