Building and Maintaining Topological Databases

AC

Link-state routing protocols, such as OSPF (Open Shortest Path First) and IS-IS (Intermediate System-to-Intermediate System), are designed to allow routers to build a complete map of the network topology. This map is then used to calculate the shortest path to any given destination. To build and maintain this topological database, routers use information from different sources.

The two sources of information that a router running a link-state protocol uses to build and maintain its topological database are:

1. Hello Packets: Hello packets are sent periodically by routers to establish and maintain neighbor relationships. Hello packets contain information about the router sending the packet, including its IP address and interface priority. These packets are used to determine if neighboring routers are still alive and to discover new neighbors.

2. Link-State Advertisements (LSAs): Link-state advertisements (LSAs) are used by routers to advertise their directly connected networks and to learn about the networks that other routers are connected to. Each router creates LSAs for each of its directly connected networks and sends these LSAs to all other routers in the network. When a router receives an LSA from another router, it updates its topological database and recalculates its routing table.

Therefore, options A and C are correct as routers running a link-state protocol use Hello Packets and LSAs from other routers to build and maintain their topological database. The other options (B, D, E, and F) are not used by routers running a link-state protocol to build and maintain their topological database.