E. Unicast Routing Protocols

There are two kinds of routing protocols available to route unicast packets:

  • Distance Vector Routing Protocol

    Distance Vector is simple routing protocol which takes routing decision on the number of hops between source and destination. A route with less number of hops is considered as the best route. Every router advertises its set best routes to other routers. Ultimately, all routers build up their network topology based on the advertisements of their peer routers,

    For example Routing Information Protocol (RIP).

  • Link State Routing Protocol

    Link State protocol is slightly complicated protocol than Distance Vector. It takes into account the states of links of all the routers in a network. This technique helps routes build a common graph of the entire network. All routers then calculate their best path for routing purposes.for example, Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (ISIS).

F. Multicast Routing Protocols

Unicast routing protocols use graphs while Multicast routing protocols use trees, i.e. spanning tree to avoid loops. The optimal tree is called shortest path spanning tree.

  • DVMRP  – Distance Vector Multicast Routing Protocol
  • MOSPF  – Multicast Open Shortest Path First
  • CBT  – Core Based Tree
  • PIM  – Protocol independent Multicast

Protocol Independent Multicast is commonly used now. It has two flavors:

  • PIM Dense ModeThis mode uses source-based trees. It is used in dense environment such as LAN.
  • PIM Sparse ModeThis mode uses shared trees. It is used in sparse environment such as WAN.

G. Routing Algorithms

The routing algorithms are as follows:


Flooding is simplest method packet forwarding. When a packet is received, the routers send it to all the interfaces except the one on which it was received. This creates too much burden on the network and lots of duplicate packets wandering in the network.

Time to Live (TTL) can be used to avoid infinite looping of packets. There exists another approach for flooding, which is called Selective Flooding to reduce the overhead on the network. In this method, the router does not flood out on all the interfaces, but selective ones.

Shortest Path

Routing decision in networks, are mostly taken on the basis of cost between source and destination. Hop count plays major role here. Shortest path is a technique which uses various algorithms to decide a path with minimum number of hops.

Common shortest path algorithms are:

  • Dijkstra’s algorithm
  • Bellman Ford algorithm
  • Floyd Warshall algorithm

Courtesy of:

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