Build a baseline
When it comes to administering your network, the first thing you have to know is whether the network is operating up to par, or not. To do that, you need to know what its performance should be like, and, to do that, you need a baseline. Intuitive hunches aren't good enough; you must be able to measure against some standard, and that's what a baseline provides. This tip, excerpted from InformIT, offers a definition of and examples from, a baseline.
Several things make up a baseline, but at its heart, a baseline is merely a snapshot of your network the way it normally acts. The least effective form of a baseline is the "sixth sense" that you develop when you've been around something for a while. It seems to work because you to notice aberrations subconsciously because you're used to the way things ought to be. Better baselines will be less informal and may include the following components:
- Network traces
- Summarized network utilization data
- Logs of work done on the network
- Maps of the network
- Records of equipment on the network and related configuration data
In Chapter 10, "Network Monitoring Tools" we discussed the ethereal network analyzer. This tool's capability to save capture files (or traces) enables you to maintain a history of your network. If the only traces you have saved represent your troubleshooting efforts, you won't have a very good picture of your network.
You also need to be aware that a lot of things will influence the contents of the traces you collect. Weekend vs. weekday; Monday or Friday vs. the rest of the week; and time of day are all examples of the kinds of factors that will affect your data. Running ethereal (or some other analyzer) at least three times a day, every day, and saving the capture file will give you a much clearer idea of how things normally work.
Several tools can give you a quick look at your network's behavior: netstat, traceroute, ping, and even the contents of your system logs are all good sources of information.
The netstat tool can show you several important bits of information. Running it with the -M, -i, and -a switches are especially helpful. I typically add the -n switch to netstat as well; this switch turns off name resolution, which is a real boon if DNS is broken or IP addresses don't resolve back to names properly. The -i switch gives you interface specific information.
The traceroute tool is especially important for servers that handle connections from disparate parts of the Internet. Setting up several traceroutes to different remote hosts can give you an indication of remote users connection speeds to your server.
The ping tool can help you watch the performance of a local or remote network in much the same way that traceroute does. It does not give as much detail, but it requires less overhead.
You will likely find yourself touching a lot of the equipment on your network, so it is important that you keep good records of what you do. Even seemingly blind trails in troubleshooting may lead you to discover information about your network. In addition, you will find that your documentation will be an invaluable aid the next time you need to troubleshoot a similar problem.
Some people like to carry around a paper notebook to keep their records in; others prefer to keep things online. Both camps have good points, many related to information access. If you keep everything in a notebook but don't have it handy, it does you no good. Similarly, if everything is online and the network is down, you're in bad shape.
A roundly ignored set of baseline information is the network map. If you have more than two systems in your network and don't have a map, set down this book for 20 minutes and sketch something out. It doesn't have to be pretty, just reasonably accurate.
You should also have accurate records of the hardware and software in your network. At a minimum, you should have a hardware listing of each box on the network, a list of system and application levels (showing currently installed versions and patches), and configurations of the same. If you keep this in cvs, you'll also have a nice mechanism for looking at your history.
If you decide to keep these records, it is vital that they be kept up-to-date. Every time you make a change, you should edit the appropriate file and commit it to permanent storage.
To read the article from which this tip is excerpted, click over to InformIT. You have to sign up there to get the article, but the registration is free.