As you know, DNS resolution maps a fully qualified domain name (FQDN), such as www.linuxhomenetworking.com, to an IP address. This is also known as a forward lookup. The reverse is also true: By performing a reverse lookup, DNS can determining the fully qualified domain name associated with an IP address.
Many different Web sites can map to a single IP address, but the reverse isn't true; an IP address can map to only one FQDN. This means that forward and reverse entries frequently don't match. The reverse DNS entries are usually the responsibility of the ISP hosting your site, so it is quite common for the reverse lookup to resolve to the ISP's domain. This isn't an important factor for most small sites, but some e-commerce applications require matching entries to operate correctly. You may have to ask your ISP to make a custom DNS change to correct this.
There are a number of commands you can use do these lookups. Linux uses the host command, for example, but Windows uses nslookup.
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