Link-State Routing Basics

Compared to distance vector routing, link-state routing improves routing structures by performing calculations on the best paths rather than simply passing the full routing table information between routers. Link-state routing sends interface information only about the various interfaces on the router and the networks to which the router is connected. Therefore, instead of sending a routing table of 20 to 50 entries, link state updates only send information about the four to six router interfaces.
Understanding the link state protocol
Each router puts all the link state information it receives into a topological database, which is a table containing link information about all known routers. do not specify the routes; Instead, it records all the information required to access each network segment connected to each router after calculating the routing information.
There will likely be more than one path per network, so it is important to evaluate every possible path to find the best path for each part of the network. You can do this using the shortest path first (SPF) algorithm, which then builds an SFP tree.
Since the router knows all the links on the network, it is able to evaluate all the links on its own to determine the most efficient way to reach every other network segment on the network. This is referred to as the shortest path for each of these network segments. All the shortest paths are stored in one place, referred to as the SFP tree.
After the SFP tree is created, the router reviews it to find the best possible path for each network. After finding the best routes, the router adds them to its routing table. This routing table is built on each router, but it should be the same for all routers that receive the same updates, because they all use the same process to create the routing table.
When a router starts up and sends its raw link state information to neighboring devices, it reduces network load by sending updates only to its link information. These LSAs are streamed to all routers in his or her region. LSAs are just updates to their link state, so one is sent whenever a link is connected or disconnected.
Work with your strengths
This update handling system appears to be the key to the strength of link state protocols. Although some variation occurs between the two protocols, in general, link state protocols differ from distance vector protocols in the following ways – you can determine if these differences represent advantages or disadvantages:
1. Cost metrics are the main determining factor for choosing a route. These cost metrics are the evaluation point for identifying the best links, which may include links speed and capacity.
2. Routing updates are less frequent.
3. High degree of scalability to support much larger networks.
4. Divide the entire network into smaller parts to limit the scope of routing changes.
5. It only sends updates about link status and structure changes.
6. Triggered updates can instantly notify systems of changes, reducing convergence times.
7. Network design can reduce the size of the link state database. When the network identifier is planned to support path summarization, reducing the number of paths will reduce the size of the link state database.
8. Limited data lifespan, because LSA aging always keeps the information up-to-date.
9. Routing loops are virtually eliminated because routers know what the entire network topology looks like.
10. Large amounts of memory are required to support not only the routing table, but also the link state database and the neighbor database (which is a table that lists the neighbors).
11. Implementation of Dijkstra’s algorithm (the mathematical formula used to perform the shortest path computation) requires the use of CPU cycles on the router, and for larger networks this requirement means that more CPU time is spent on the calculations.
12. In large network applications, link-state protocols can require a great deal of tuning to function properly. This necessity can pose significant challenges to the network administrator.
If you have enough CPU and memory resources on your network routers and your network layout isn’t overly complex, you shouldn’t have problems with link-state protocols – you’ll only reap the benefits. There is no reason why link state protocols cannot be used as the primary routing protocol on your network.