
Editing the Configuration Files
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The Reverse Zone File
With our primary zone file completed, programs can look up the centralsoft.org
domain and all its subdomains in DNS. But we still need a reverse zone file.
A reverse zone file maps IP addresses to names. It looks almost like a mirror of the
primary zone file; instead of listing the names first, the reverse zone file lists the IP
addresses first.
Why might someone use a reverse zone file? In the past, many organizations would
refuse to allow you to use their services if they could not ping your domain name in
reverse. Today, many Internet servers use reverse lookups to verify the origins of
email to stop spammers; this is the purpose of the
SPF records discussed earlier.
The system we’ve described here deals with a mail-relaying problem that will be
explained further in Chapter 5. DNS indicates which MTA is responsible for mail
from the domain listed in the email sender’s address. Many spammers try to relay
mail using different MTAs, but the receiving mail agent can do a reverse lookup, spot
the irregularity, and refuse the unwanted email.
Since we don’t want emails originating from the centralsoft.org domain to be classi-
fied as spam, we’ll create a reverse zone file. First, to point to this file, we have to
place this entry in our named.conf file:
zone "158.253.70.in-addr.arpa" {
type master;
file "pri.158.253.70.in-addr.arpa";
};
The numbers ...