Link State Routing Protocol

Link State Routing Protocol:
Link mean an interface on a router and state is the information and state of the links. Information and state of an interface include
ü  IP address
ü  Subnet mask
ü  Type of network
ü  Cost associated with link
ü  Neighboring routers on the link

In Link state routing protocol state of any link is forward to neighbor, through which every router create a full map of network. Link state use the multicast instead of broadcast. In packet switching network there are two link state routing protocol i.e. Open Shortest Path First (OSPF), Intermediate System-Intermediate System (IS-IS)

How Link state routing protocol works:
1.       Link state process starts with learning it’s directly connect router.
2.       Link state routers exchange hello packet and Connected link state routers
3.       Each router builds its own Link State Packet (LSP) which includes information about neighbors such as neighbor ID, link type, & bandwidth and floods it to all neighbors who then store the information and then forward it until all routers have the same information.
4.       Routers use LSP database to build a network topology map & calculate the best path to each destination.
LSPs are sent out under the following conditions:
        i.            When routing process starts
      ii.            When there is a change in topology
Every router that connects to a given OSPF area should learn the exact same topology data. Each router creates a link state database (LSDB) using LSAs. Then, the router uses the Shortest Path First (SPF) algorithm to find the best path.

Determining the shortest path
The shortest path to a destination determined by adding the costs & finding the lowest cost

link state routing protocol Requirements:

Typically link state routing protocols use more memory, CPU processing and need lots of bandwidth for Initial startup of link state routing protocols.

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