The Routing Information Protocol ( RIP )
I will summarize Request For Comments (RFC) 1058, Routing Information Protocol (RIP), by discussing RIPs basic algorithm/distance vector algorithm, protocol, message format, protocol limitations, and new improvements to RIP.
RIP is very important to internetworking, since it passes information about routes between networks and hosts. It allows hosts and gateways to exchange information for the purpose of computing routes.
BASIC ALGORITHM/DISTANCE VECTOR ALGORITHM:
RIP was designed to work with moderate sized networks, which used pretty much the same technology. It was not intended to work complex network systems. RIP is widely used for routing traffic in the global Internet and is an interior gateway protocol (IGP), which means that it performs routing within a single autonomous system.
On the Internet, an autonomous system is either a single network or a group of networks that are controlled by a common network administrator (or group of administrators) on behalf of a single administrative entity (such as a university, a business enterprise, or a business division). An autonomous system is also sometimes referred to as a routing domain.
There are several algorithms to determine routes between networks. One categorization is on the type of information that is needed to be exchanged between the networks. Distance vector algorithms exchange only a small amount of data. Each participating gateway keeps information about all destinations within the network.
RIP is a "distance vector algorithm". The basic distance vector algorithm attempts to find the shortest number of "hops" possible to reach the destination. A hop is whenever you pass through a node. In the following example the distance from X to Z is 2:
X ----- Y ----- Z
When the network has many interconnected nodes, the shortest distance is harder to find. In the following, the distance could be 4,5,6 and more.
/ / |
/ / D---E
F-----G | |
| H |
| / |
/ | |
In the above, the shortest path from A to M could be A-B-C-E-M, A-B-D-H-M, or A-G-J-L-M. There are two algorithms that find the shortest path: the Bellman-Ford or Dijkstra algorithms. Once one of these algorithms are run, each node in the network will know the shortest path from itself to each other node in the network.
The algorithm uses fixed "metrics" for route comparisons. The fixed metrics could be time delay, cost, or some other value used to compare routes. In the following network, the numbers represent the cost to transverse the link.
A ---- 1 ---- B ----- 2 ----- C