Changes in the RIP Protocol topology-convergence

So far, the basic mechanisms and features of r I P have been discussed in a rather static manner. However, by examining how these mechanisms interact with each other to adapt to network topology changes, we can gain a deeper understanding of the r I P mechanisms.

Convergence
The most important result of the topological change in the r I P network is that it changes the adjacent node set. This change also leads to different results for the next distance vector calculation. Therefore, the new adjacent node set must be aggregated from different starting points to the new topology, the process for obtaining a consistent topology view is called convergence (c o n v e rg e n c e ). To put it simply, convergence means that the router obtains a common view of the network structure independently.

Figure 1 2-9 shows the convergence process. The figure shows two possible routes from router A and network 1 9 2. 1 6 8. 1 2 5 to router D. Vrod D is a gateway router. The basic route to vrod D must pass through vroc C. If this router fails, it will take some time for all routers to converge to the new topology, which does not include the link between router C and router D.

If the link between router C and router D fails, it will no longer be available, but it takes quite some time for the entire network to know this fact. The first step of convergence is that D recognizes that the link to C is faulty. Assume that the update timer of vrod D expires before the timer of vrod C. Because this link should have transmitted the update packet from router D to router C, C cannot receive the update packet sent by router D. C (A and B) is still unaware that the C-D link has failed. All vrouters in the interconnected network will continue to forward packets destined for vrod D through that link. The first phase of convergence is shown in Figure 1 2-1 0.

Figure 12-9 two possible paths from vroa A to vrod D

Figure 12-10 only vrod D is aware of LINK FAILURE

Once the update timer times out, vrod D tries to notify its adjacent vro of network topology changes. Only vrob B can directly contact the directly adjacent users. When an update packet is received, B updates its route table and sets the route from B to D (through C) to infinite. This allows it to communicate with D through the B-D link. Once B updates its route
It broadcasts new changes to the topology to other adjacent users, A and C.

Note that setting the route measurement to 16 for a RIP node invalidates a route.-16 is equivalent to infinite for RIP nodes.

Once A and C receive the update packet and re-calculate the network consumption, they can use the B-D link to replace the table items using the C-D link in the routing table. In the past, all nodes, including B-D nodes, did not use B-D routing because it was more expensive than the C-D link. The cost measurement is 1 0, and the cost of C-D is 1. Now, when the C-D link fails, the consumption of the B-D link becomes the lowest. Therefore, this new route replaces the router that times out in the route table of adjacent nodes.

When all routers realize that B is the most effective route to D, they converge, as shown in 1 2-11.

Figure 12-11 routers use B-D as a new route

It is not easy to determine the time required before convergence is completed. It varies greatly by network, depending on many factors, including the robustness of routers and transmission lines, and traffic flow.

Related Articles]

• RIP Operation Mechanism

• RIP Distance Vector Algorithm

• The RIP Protocol calculates the value to infinity.