Link State vs Distance Vector Protocols

In this CCNA and CCNP ENCOR lesson, we will compare link state vs distance vector protocols. We will start with what is distance vector protocols and link state protocols and then we will see the differences of link state and distance vector protocols. We will also compare two important routing protocols OSPF and EIGRP as EIGRP vs OSPF comparison.

At the end of this lesson, you will find an updated comparison table for these two routing protocols.

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What is Distance Vector Protocol?

Distance vector routing protocols are the protocols which uses distance (cost) to determine the best path as its name implies. There are three important routing protocols for network engineers are distance vector protocols. These are: RIP (Routing Information Protocol), IGRP (Interior Gateway Routing Protocol), and EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP also named as advanced distance vector protocol or hybrid protocol.

RIP and IGRP is not used too much in today’s networks. But EIGRP is still a popular routing protocol.

What are the characteristics of distance vector protocols? As we have explained above, distance vector protocols use distance (cost) to determine the best path. This distance (cost) can be hop, delay, etc. They also use outgoing interface to determine the best path. The name of these protocols also implies this: distance-vector. Here, vector shows the direction.

Two distance vector protocols, RIP and IGRP use Bellman-Ford Algorithm to calculate the shortest paths to various destination. On the other hand, EIGRP is an advanced distance vector protocol. So, it uses another algorithm for route calculation. The name of EIGRP algorithm is DUAL Algorithm.

Each router maintains a routing table which includes the best paths to the destinations. And each router exchanges their routing table with its neighbors periodically if they are using distance vector protocols. In other words, distance vector protocols use periodic updates. They see the network from the perspective of their neighbors.

By the way, it is easy to configure distance vector protocols but they are not as effective as link-state protocols. Their periodic and limited updates consume resources too much and this results higher convergence times. So, these protocols can be used in small networks instead of large networks.

What is Advanced Distance Vector Protocol?

RIP and IGRP are two distance vector protocols. But EIGRP is an advanced distance vector protocol. Because, it has some enhancements over the previous distance vector protocols, RIP and IGRP. The algorithm used by EIGRP is also different. EIGRP uses DUAL Algorithm while RIP and IGRP use Bellman-Ford Algorithm.

What is Link-State Protocol?

Link-State routing protocols are the routing protocols which exchanges detailed information between routers. OSPF (Open Shortest Path First) and IS-IS (Intermediate System to Intermediate System) are two link-state protocols. These protocols are strong and they have good convergence times.

How does a link-state protocol work? In each router there is a Link Sate Database named LSDB. With this link state database, many information about the network is stored. This information is directly connected networks, the states of the links, costs etc. Each router exchange LSAs and inform the other router in the network. So, every router in the network has a full view of the network.

Link State Routing Protocols use different Tables. These are Topology Table, Neighbor Table and Routing Table.

The updates of Link State Routing Protocols are triggered not periodic like Distance Vector Protocols.

Link-state routing protocols are a little difficult to implement if you compare with distance vector protocols. But they effective with their fast convergence times.  So, these protocols can be used in large networks.

What is Hybrid Protocol?

Hybrid protocol is a term used for EIGRP (Enhanced Interior Gateway Routing Protocol). EIGRP is not a complete distance vector protocol in real. It is a protocol which has both distance vector and link-state protocol characteristics. So, the answer of what is Hybrid protocol is it is EIGRP.

Distance Vector vs Link State Protocols

We have learned what is distance-vector protocol and what is link-state protocol. Now, it is time to compare link-state vs distance vector protocols. Below, you will also find a comparison table for these two routing protocols.

Let’s start with the protocols of these categories. RIP and IGRP are distance vector protocols while OSPF and IS-IS are in link-state category. EIGRP is a hybrid protocol or in the category of advanced distance vector protocol.

Distance vector protocols are good for small networks while link state protocols are used in large networks. Especially OSPF and IS-IS protocols are good for ISP (Internet Service Provider) networks.

Distance vector protocols see the network from the neighbor’s perspective while link-state protocols have the complete network view.

In distance vector protocols, only periodic updates are used and these updates has entire routing table information. On the other hand, link-state protocols use triggered updates and they send only the changes.

Link-State vs Distance Vector Protocols

Another difference on link-state vs distance vector protocols is about convergence time. The convergence time of distance vector protocols is slow while link-state protocol’s convergence time is fast.

The maintenance and configuration are easy for distance vector protocols while it is harder to configure and maintenance link-state protocols.

Distance vector vs link-state protocols also differ on bandwidth and memory usage. Distance vector protocols need more bandwidth and less memory while link-state protocols need less bandwidth and more memory.

The used route calculation algorithm is also different for distance vector and link-state protocols. Distance vector protocols, RIP and IGRP, use Bellman-Ford Algorithm. Link-State protocols, OSPF and IS-IS use Dijkstra Algorithm.  Advanced distance vector protocol or Hybrid protocol EIGRP use DUAL Algorithm.

Comparison of Routing Protocols

Here, we have talked about link-state vs distance vector protocols. We have compared RIP and IGRP with OSPF and IS-IS. Another comparison lesson is EIGRP vs OSPF lesson. In other words, advanced distance vector vs link-state protocols. You can also check this lesson to learn more about these routing protocols. This lesson is important for Cisco CCNA and the other lesson is important for Cisco CCNP ENCOR Exams.

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