Red Hat Linux 7 Unleashed

Red Hat Linux 7 Unleashed

By William Ball

A Word About This Chapter's Examples

The examples in this chapter were created to illustrate specific points and to allow you to safely run them on a two-computer network. To accomplish this with minimal risk to the worldwide DNS system or your company's DNS system, all examples use the imaginary top-level domain name .cxm.

In addition, all examples use private IP subnet 192.168.100. This is one of the subnets set aside for local, non-Internet use. You can see the complete list of private IP subnets in RFC 1918, mirrored at http://www.isi.edu/in-notes/rfc1918.txt. If, by chance, your company already uses the 192.168.100 numbers for in-house IP addresses, you must pick another private subnet for this chapter's examples.

If running this chapter's examples happens to release any information to a higher level or the worldwide DNS, the bogus top level domain and the private IP numbers would instantly brand it as garbage to be ignored. Of course, if you're doing a genuine Internet-connected DNS instead of the chapter examples, use the domain name and IP address assigned to your organization by the proper authorities.

DNS is complex, and it is one of the few systems on your network that depends intimately on the correct working of machines elsewhere. Likewise, machines elsewhere depend intimately on the correct working of your DNS system. In the world of real top-level domains and public IP addressees, an unnoticed error in your DNS setup can cause serious problems for other people thousands of miles away, which in turn may cause serious problems for you.

When doing real-world DNS, please keep these rules in mind:

In order to best illustrate specific points, this chapter's examples do not consistently follow all these rules. I suggest that if you want to run this chapter's examples, you do so on a pair of machines not presently serving DNS for your organization, and make sure to use the bogus .cxm top-level domain and the private 192.168.100 subnet.

NOTE

Any time you observe excessively slow telnet connections (greater than 5 seconds to get the logon prompt), suspect dysfunctional DNS resolution, probably reverse resolution. In such cases, it's simple to configure forward and reverse resolution by following the instructions in the Configuring DNS Server Master Zones section later in this chapter.

CAUTION

Before editing any configuration file, back it up. Original distribution or installation-default files should be backed up to files with .org appended to the end (such as http://resolv.conf.org). Other revisions can be backed up with the naming convention of your choice, as long as they don't overwrite the .org files. Take care never to change or overwrite an .org file.

Share ThisShare This

Informit Network