Four defects limit the use range of the RIP routing protocol (1)

When deploying a large network, the network administrator has a headache, that is, how to select a suitable routing protocol. Because different routing protocols have different design ideas, their performance and functions are different. Selecting an appropriate routing protocol can improve network performance and stability. However, it is not easy to select a suitable routing protocol, just like choosing a lifelong partner. I will analyze the restrictions on the use of the RIP Routing Protocol to help the network administrator use this routing protocol when appropriate.

RIP is short for routing information protocol. This routing protocol is the first of other routing protocols and has been standardized as a public standard routing protocol. RIP is a simple distance vector routing protocol, and the standard of this Protocol is open, so now basically all routing devices support this RIP protocol. Although basically all network devices support this RIP routing protocol, it does not mean that it can be used in all scenarios. Due to its inherent defects, there are still many restrictions on its use scope.

Defect 1: hop count limit

During the design of the RIP routing information protocol, it is mainly used to handle Routing Problems in small networks. Therefore, it has a limit on the maximum number of hops. Currently, the maximum number of hops supported by the RIP Protocol is 15. When the RIP route information protocol forwards data, the hop count of the Data Group increases the link cost. The default value is 1. If the maximum number of hops of a Data Group reaches 15 and the Data Group has not reached the destination, the Data Group will be discarded. The router will think that the destination cannot be large because it has exceeded the maximum number of hops. However, the destination may be on the hop side.

Defect 2: Slow Aggregation

Aggregation refers to a mechanism by which routers reach an agreement on the new network topology. When the network topology changes, each vro must aggregate the changes. If the neighboring router changes, the router needs to adjust its route table information through the aggregation mechanism. Therefore, the speed of this aggregation process is directly related to the stability of the network. In order to ensure the smooth progress of this aggregation, a mechanism such as triggering update and restraining timer is adopted in the RIP routing information protocol. The update trigger is used to accelerate the aggregation process of the RIP route network. Generally, the router sends an update message at an interval of 30 seconds. After the update trigger mechanism is adopted, the router immediately broadcasts an update message as long as the network topology structure changes. After an update is triggered, the aggregation process can be accelerated to a certain extent. However, time is still a problem. Because all routers on the Internet cannot receive messages within a reasonable period of time and update their route tables. Therefore, in the RIP routing information protocol, a timer suppression solution is proposed. The suppression timer solves the potential problems with triggering updates. That is to say, after an update is triggered, the router starts a suppression timer. Before the timer reaches 0, the router will not accept any updates to the faulty route from the neighboring router. The suppression timer can effectively prevent routers from accepting and aggregating invalid routes for a certain period of time. The suppression timer prevents the router from believing that other routers have a route to an invalid destination within a period of time.

Although the RIP Protocol has taken some measures to ensure the effectiveness of the aggregation process, it still cannot effectively solve the problem of slow aggregation. The RIP route information protocol usually sends route update information every 30 seconds. This time interval may not be long in the eyes of ordinary people. However, in the online world, this time is a long time. A metaphor for an image is that one second in the human world is like one day in the online world. Therefore, during these 30 seconds, many things will happen in the online world, such as damage to the router or congestion in the transmission path. However, it takes 180 seconds for a single RIP Router to declare its failure. The interval is too long. As the enterprise network structure becomes increasingly complex, the aggregation time will grow. This will directly affect the network stability.

Defect 3: route table update data occupies valuable network bandwidth

The routing protocol is mainly used to solve the problem of changing the network topology. Generally, the router sends a route information table to other routers at a fixed time to indicate their possible destinations. However, each vro protocol has its own ideas about how much content is transmitted. After all, this update information needs to be transmitted over the network, which will occupy the network bandwidth. If only necessary information is transmitted when route update information is transmitted, the negative impact of route update information on network performance can be reduced. You know, if the network is complex, the capacity of the route update information will be large and will occupy a large amount of network bandwidth. In fact, if you only need to change some of the network topology, for example, you only need to add a vro on a certain link. The routing information that this affects is actually very limited. If this update message is sent to all routers at this time, including the unaffected router devices, it may be repeated.

The same is true for the RIP routing information protocol. Normally, the RIP Router broadcasts the entire route table to all interfaces with RIP enabled every 30 seconds, instead of only broadcasting the affected route. In a large network, this update will occupy a large amount of valuable bandwidth, which can be used to transmit data packets. This will greatly reduce network performance. The more complex the network is, the greater the capacity of route update information, the greater the negative impact.