Routing Information Protocol
Routing Information Protocol is a distance-vector, Interior Gateway Protocol (IGP) which is used by routers to exchange routing information. RIP prevents routing loops by implementing a limit on the number of hops. RIP uses hop count to determine the best path between two locations. Hop count is the number of routers the packet must go through till it reaches the destination network, the maximum number of hop count of 15 by default, which means a hop count of 16 is considered an infinite distance, and the route is considered unreachable. RIP works well in small networks, but it’s inefficient on large networks with slow WAN links or on networks with a large number of routers installed. RIP uses the User Datagram Protocol (UDP) as its transport protocol and is assigned the reserved port number 520.
RIP Timers
Update timer: It is an interval of 30 seconds between two routing update. Each RIP enables the router to send its complete routing table to all neighboring routers every 30 seconds. This method is called a periodic update method.
Invalid/Hold timer: Invalid time define how much longer a router should wait for an update from the neighboring router. It is usually 180 seconds. If a router does not receive any update from a specific neighbor for 180 seconds then the router is declared as dead and all routes from that router are declared as invalid. Invalid times do not remove any entry from the routing table by marking it as invalid for a specific period for time.
Flush timer: Flush timer is the time between a route becoming invalid and its removal from the routing table, which is 240 seconds.
Versions
There are of the Routing Information Protocol: RIPv1, RIPv2, RIPng.
RIP version 1: RIPv1 does not carry subnet information, lacking support for variable-length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside the same network class. All subnet in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.
RIP version 2: Due to the deficiencies of the original RIP specification, RIP version 2 was developed. It includes the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). RIPv2 multicast the entire routing table to all adjacent routers at the address 224.0.0.9, as opposed to RIPv1 which uses broadcast. Unicast addressing is still allowed for special applications. Router tags were also added to RIP version 2.
RIPng: RIPng (RIP next generation) is an extension of RIPv2 for support of IPv6, the next-generation Internet Protocol.
Classful routing protocol. No subnet mask information is transmitted with the routing updates
Classless routing protocol. Sends subnet mask with the routing updates.
Uses broadcast to send a routing update
Uses multicast to send routing update
Does not support VLSM
Support VLSM
Does not support authentication of the update message
Support both plain text and MD5 authentication mechanism
Syntax:
Router(config)# router rip
Router(config-router)# network x.x.x.x
Router(config-router)# network x.x.x.x
Router(config-router)# version 2
To configure RIP on router A we use the following command
Router A(config)# router rip
Router A(config-router)# network 192.168.0.0
Router A(config-router)# network 192.168.1.0
Router(config-router)# version 2
Originally published at https://eiheducation.in on June 2, 2019.