Step4 Check for Recent Changes

Recent changes are not always responsible for problems that occur, but they should always be examined as a potential cause of the problems. The reason for this is simple: Today's networks are so complex that it is difficult to ensure that a change does not cause a problem for a dependent system. Consequentially, it is critical that you have a means of tracking and monitoring the changes that are made in your environment so that you have something that you can refer back to.

Good change control is more than just "busy work." It provides a methodical means of answering the questions of who, what, and when:

• Who made recent changes At the most simplistic, this gives you the name of who to check with regarding the changes to determine whether they can provide insight into the problem.

• What were the changes that were made This is the most important information that your change-control process contains. This information enables you to look at what was changed to make a decision as to whether it looks like the changes could be responsible for the problems. For example, if someone updated the SNMP settings but the problem appears to be with traffic being blocked, a good chance exists that the changes that were made are irrelevant for the problem that is occurring.

• When were the changes made Changes that were made days or weeks ago probably are not responsible for the problems of today. Similarly, however, if the changes were made an hour ago, and the problem showed up an hour ago, it is probably worth investigating the changes in more detail.

It is important to view recent changes as a culprit for problems with a skeptical eye, however. Before spending time undoing the changes, examine the change in the context of the problem and make sure that it makes sense for the changes that were made to be a cause of the problem. For example, one time I watched a company roll back a series of virus Digital Audio Tape (DAT) files because they were the last change made on the network before authentication errors started occurring. Now, anyone who knows anything about DAT updates knows that they have pretty much nothing to do with authentication, and this case was no different. When it was all said and done, the DAT updates were rolled back and the problem still existed, but the company lost hours of time that could have been spent fixing the problem. It was subsequently discovered that a domain controller in error was causing the problems. The point is, make sure that the changes appear to be relevant before devoting full attention to them. Just because there were recent changes does not mean that they are responsible for the problem. This is particularly true with firewalls, where it seems like if a change has been made to a firewall within six months of a problem occurring, someone will immediately question whether the firewall is the problemeven if the problem traffic in question never goes through the firewall.

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