Advantages of Address Aggregation and Key Characteristics of Routing Protocols

Discuss the advantages of address aggregation (summarization) with respect to routing table size, routing update exchange, and routing optimization?

Route aggregation and subnetting shrink the size of routing tables used by routers. Without CIDR, a router must maintain many individual entries for routes within the same network. CIDR guarantees more efficient routing and reduces the number of CPU cycles when updating a routing table. It also reduces router memory requirements.

What are the key characteristics or requirements that should be fulfilled by any routing protocol?

A routing protocol should guarantee loop-free paths, calculate multi-hop optimal paths, use simple or composite network metrics, be scalable, converge rapidly, use network resources efficiently (e.g., network bandwidth), be secure, and be a standard adopted by IETF (desired feature).

Discuss the main differences between Link-State Routing Protocols and Distance Vector Routing Protocols?

With distance vector routing protocols, a router broadcasts its entire routing table to all its directly connected neighbors. However, with a link-state routing protocol, the router sends only information about its directly connected links but floods this information throughout the network area. Distance vector protocols usually use a variant of the Bellman-Ford algorithm, whereas link-state protocols use a variant of the Dijkstra Algorithm. Link-state protocols such as OSPF are more scalable than distance vector protocols such as RIP and IGRP. Distance Vector protocols usually use a flat topology, whereas link-state routing protocols use a hierarchical structured topology.

What are the three key phases that any routing protocol should contain?

Any routing protocol contains at least 3 phases or processes: A Discovery Process: Router advertises itself and its parameters to local hosts and neighboring routers and establishes or does not establish adjacencies with them (handshake). A Routing Update Process: Partial or Full update of the routing table. Maintenance Process: Maintain both reachability with neighboring routers and maintain up-to-date routing information.

Identify and describe the five major types of Link State Advertisements (LSAs) which can occur in OSPF?

Type 1 router LSAs – generated by each router for each area it is in. They are only flooded within an area. Type 2 network LSAs – generated by Designated Routers and describe the set of routers attached to a particular network. They are flooded in the area that contains the network. Type 3 summary LSAs for ABRs – generated by ABRs and describe inter-area routes to various networks. They can also be used for aggregating routes. Type 4 summary LSAs for ASBRs – describe links to ASBRs and are generated by ABRs. Type 5 autonomous system external LSAs – generated by ASBR. They describe routes to destinations external to the AS. They will be flooded everywhere except stub areas.