 Hello and welcome to a lecture on routing information protocol. Learning outcomes. By the end of the session, student will be able to illustrate routing information protocol and its message format. Here you may pause the video and try to answer this question. What are the solutions to count to infinity problem? This problem is with the distance vector routing algorithm. The three possible solutions to count to infinity problem are redefining the infinity, means maximum number of hops the packet can travel is made to 16. 16 hop is considered as not reachable. The split horizon and split horizon with Poisson reverse. These are the three possible solutions to count to infinity problem. Let us see the routing information protocol. Routing information protocol is an intra domain routing protocol based on distance vector routing means this routing information protocol handles or look after the routing inside an autonomous system. The routing information protocol implements the distance vector routing algorithm with following consideration. The first consideration is in an autonomous system the RIP deals in graph theory with routers representing the nodes and the arcs represent the links. The destination network in routing table is a network address. The metric used by routing information protocol is hop count. The infinity is redefined as 16. The next node column of the routing table describes the address of the router to which the packet is to be sent so that it reaches its destination. Let us understand how the routing table looks like in routing information protocol and what are its fields and how it describes the route to a particular network. Here we have four routers R1, R2, this is R2, R3 and R4 with seven networks N1, N2, N3, N4 and N5, N6 and N7 means we have four routers R1, R2, R3, R4 and network N1, N2, N3, N4 and these networks are connected to any of the router. Let us understand this is a routing table of router R1 and let us understand the entries as N1 and N2, network N1 and N2 are directly connected to R1 so the cost or the distance to these two network will be 1. In the first two entries of this routing table you can see that network N1 and N2 has cost of 1 and in the next hop column there is no entry because as these two networks are directly connected. For network N3, N4 and N5 to deliver a packet to N3, N4 and N5 router R1 has needs to forward the packet to network R2 means for network N3, N4 and N5 the next hop for R1 is router R2. So these are the three entries for network N2, sorry N3, N4 and N5 with cost increased by 1 as for network N3 a packet has to travel two networks N1 and N3 so the cost is 2 and in next hop column of the routing table the IP address to which this interface of router R2 is connected. The IP address of this interface is 130.10.0.1 so this is the next hop for all the networks N3, N4 and N5. Similarly let's check the last two entries which are for these two networks network N6 and network N7 with next hop entry with next hop as a this IP address which is 1 130.11.0.1 so in this way the routing tables are updated. Let's see the message format of routing information protocol this is a message format of routing information protocol the first field is a 8 bit command field. This field gives the type of the message whether it is a request message or a reply message for request message it has value 1 for reply message or respond response message it has value 2 this is a version field it is also 8 bit field this 8 bit field gives the version of routing information protocol routing information protocol comes with two version version 1 and version 2. So according to the version you are using this value this field contains value 1 or 2 the next 16 bit field is reserved field it is not used then the next field is a 16 bit family field this 16 bit field defines the protocols used for TCP IP protocol this field contains value 2 then we have these four this two byte these four bytes this also four byte and this four byte these four blocks out of which these three are each of four bytes so it becomes 12 and these two means total 14 byte field for network address okay for IP internet protocol for internet protocol only four bytes out of 14 are used to give the destination network address and the remaining 10 bytes are filled with zero as all zeros as written in this diagram okay then the last last field is distance which is nothing but a metric for routing information protocol number of hops is a metric so this field contains the distance to the destination network from the advertising router the request message has value 1 in the first field and when a request message is generated a request message is generated when the router comes up or a some timer expires a request message can be generated for some of the networks as shown in this figure a and it can be generated to request all the network entries from router so when the request message is generated for all the entries from router the network address field contains all zeros and when it is made for specific network the network address of that specific network comes in this field the response packet how the response packet look like just to this request packet one additional distance field okay this distance field is added where the distance to the destination network is at so it becomes your response packet okay the response packet can be either solicited or unsolicited a solicited response is sent only in answer to a request made by a router it contains information about the destination specified in the corresponding request on the other hand unsolicited response is sent periodically every 30 seconds or whenever there is a change in the routing table unsolicited response is sent out this unsolicited response is sometime is also called an update packet so whenever the update packet is received by the router the router updates its routing table based on the information received in the update let's see the timers in routing information protocol routing information protocol has three timers periodic timers expiration timer and garbage collection timer the periodic timer is set randomly between 25 seconds 35 seconds the expiration timer is of 180 seconds and the garbage collection timer is of 120 seconds periodic updates are generated once this timer expire the expiration timer wait for 180 seconds and if the update for that route is not received it just mark that route as a invalid or not reachable once the route to that specific network is marked as invalid it is not directly removed from the routing table rather the router waits for 120 seconds so that the invalidity of the route propagates to all of its neighbor so these three timers support the operation of routing information protocol these are the references used and thank you