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Overview: RIP basics

Goal: Visualize RIP configuration and exchanging of Request and Reponse to discover new routes.
Topology: Two hosts H1 and G2 are connected to two RIP routers as H1-R1-R2-H2.
Steps: 1) Configure R1 IP address and start RIP. (R2 has already started RIP. )
            2) R1 and R2 flood Request and R2 to exchange routing information. 
            3）H1 ping H2 is successful.

Configure IP address

First, configure the IP addresses for R1 and R2's interfaces. 
See actual commands in R1's command line window.

R1: Start RIP, flood Request

Start RIP at R1. It floods Request to all ports immediately.  Yjere are two types of RIP packets: 
- Request. R1 sends Request to ask its neighbors their routing information. 
- Response. A RIP router sends Response periodically to neighbors of its routing information.

R2: return Response

When R2 receives R1's Request, it sends its routing data in a Response to R1.

R1: update routing table

When R1 receives Response from R2, it discovers a new destination 192.168.1.0 and adds a new entry  (R, 192.168.1.0/24, E0/0) to its rotuing tabe.
Note: In the routing table, Type is C for directly connected networks. Type is R  for RIP routes.

R1: flood Response

Now R1 floods a Response which contains R1's routing data.
Note: In real wirkd, after starting RIP, the router floods a Request and a Response at the same time. In this scenario, we flood Request first to ckarify the transaction.

R2: update routing table

When R2 recevies Response from R1, it adds a new route (R, 192.168.1.0/24, E0/0”) to its routing table.

H1 Ping H2

此时R1和R2都有了完整的路由表。H1 ping H2，Ping通了。

Appendix: FAQ

1. What is RIP?
Answer:  RIP is a distance vector routing protocol. It learns remote network addressesby exchanging route information with neighbors. If there are several paths to reach a destination, the path with minimum number of hops (distance) is choosen. Before RIP, routes are configured manually on each router. It is a tedious and error prone task. RIP is a simple and effective way to replace statiuc route.

2. How does RIP work?
Answer: RIP routers exchange their routing data with their neighbors. After a while, they discover remote network addresses  from neighbors' neighbors. A RIP router floods Response to its neighbors.
Response contains the router's routing data.

3. How does RIP calculate routes?
Answer: RIP uses hop count as cost metric. After flooding Responses to neighbors and their neighbors, the router discover new addresses and the number of hops to reach these addresses. When.