Isolate a Broken Network Connection

Purpose

By applying the standard four-step process illustrated in Figure 5, you can isolate a failed node in the network.

Figure 5: Process for Diagnosing Problems in Your Network

Before you embark on the four-step process, however, it is important that you are prepared for the inevitable problems that occur on all networks. While you might find a solution to a problem by simply trying a variety of actions, you can reach an appropriate solution more quickly if you are systematic in your approach to the maintenance and monitoring of your network. To prepare for problems on your network, understand how the network functions under normal conditions, have records of baseline network activity, and carefully observe the behavior of your network during a problem situation.

Figure 6 shows the network topology used in this section to illustrate the process of diagnosing problems in a network.

Figure 6: Network with a Problem

The network in Figure 6 consists of two autonomous systems (ASs). AS 65001 includes two routers, and AS 65002 includes three routers. The border router (R1) in AS 65001 announces aggregated prefixes 100.100/24 to the AS 65002 network. The problem in this network is that R6 does not have access to R5 because of a loop between R2 and R6.

Steps To Take

To isolate a failed connection in your network, follow these steps:

1. Identify the Symptoms
2. Isolate the Causes
3. Take Appropriate Action
4. Evaluate the Solution