Configure And Verify Manual and Autosummarization With Any Routing Protocol

Exam: Cisco 200-301 - Cisco Certified Network Associate (CCNA)

One important topic in 300-101 Route exam is Layer 3 technologies. Under this topic you will find many sub topics one such topic is – “Configure and verify manual and autosummarization with any routing protocol”. We will try to look into all the aspects of this topic from the CCNP exam point of view in this chapter. We hope that you will find this article interesting and informative.

This is a topic that is a major part of the EIGRP (enhanced interior gateway routing protocol). This is an interior gateway protocol that can be found in many different media and topologies. We have had a lot of articles on this too. The EIGRP will give a good coverage times with least minimal network traffic. Let us now understand how the EIGRP actually works. Well it has a lot of advantages and they are as follows:

It uses very little of the network resources. It only allows the hello packets to be transferred.
Only certain parts of the routing table changes in this case when there is a change. As a result the load on the routing protocol reduces.
You will also find at times that there is a rapid coverage the coverage is very instantaneous.

The EIGRP will depend on DUAL (diffused update algorithm) in order to calculate the shortest distance in the network. A lot of changes have been made to the protocol so the one that we have now is quite a revised form of the protocol. The EIGRP works on a simple logic it tries to find the best and the shortest path and then work. The information of the best path is stored in the protocol. It clears the bad paths in order to ensure that the lost paths can also be recovered. The system is such that only that information that is needed is only given. This makes the protocol a very efficient and effective one.

The EIGRP ensures that there is no confusion with information. No extra or unnecessary information are transferred instead it only sends updates when there has been a change in the paths. The neighbours in this network are reliable and they on time inform if there has been any changes in the routes and the paths. The EIGRP will send hello packets in every five seconds if the bandwidth is very high and it will send one every sixty second if the bandwidth is low.

This is also called the hello interval. You can also change the hello interval per interface by using the command ip hello – interval EIGRP. There is no direct way of determining the hello interval in any router; you can only make a guess about it from the output that you will get using the command show ip eigrp neighbours.

Some things that you must know about the EIGRP as a network administrator are that all the EIGRP traffic is sourced from the very primary address of the interface. There is no limit to the number of neighbours that the EIGRP can support. However, you need to see the topology complexity, the memory capacity, the processing power and the network stability before you decide how many neighbours the EIGRP will be made to support. Based on these points of you decide you will be able to ensure that the protocol is performing well.

The EIGRP will use the minimum bandwidth on the path to the particular destination in order to get the total delay in the routing metric. You can configure some other metrics too but we do not recommend that. Too many metrics and other types of metrics can cause the routing to loop in the network.

The interface of the routers in the patch to the destination will determine the delay metrics. The simple formula that you must remember about the EIGRP is that metric = bandwidth + delay. The Cisco routers will not perform any floating point math this is why you will have to round to the nearest integer.

Some common concepts that you must know about the EIGRP are feasible distance. It is the best metric along a path that will lead to the destination. The reported distance is the total metric along a path to reach the destination. The feasible successor will be the path that has a reported distance that is less than the best path at present.

It is interesting to know how EIGRP will decide if the path is loop free. To do this the protocol will have to use the concept of the feasible successor, reported distance and feasible distance. All these work together to help decide if the path is a feasible one or not. Using the concept of split horizon the EIRGP will avoid routing loops.

The EIGRP uses two types of summarization. They are auto summarization and manual summarization. We will try to discuss both in details in this chapter so that the readers get a better idea of what we are trying to say.

The auto summarization as the name itself suggests happens automatically. It will happen when whenever the border is crossed between two different networks. This is automatically performed by the EIGRP.

The autosummarization can be also done on external routes. The EIGRP will not auto summarise the external routes until and unless there is a component of the same major network that can be found in the internal route. This is done by using the redistribute connect command.

We will now discuss the manual autosummurization so that the readers can get a better idea on this topic. In this case the EIGRP will allow the network administrator to summarise the external and the internal routes on virtually any bit boundary. This can be done using the manual summarization. For doing this you will need the command ip summary address eigrp that will be used under the interface serial 0.

We hope that this discussion on “Configure and verify manual and autosummarization with any routing protocol” was interesting and it did improve your knowledge on the topic.

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