Configuring and Managing MPE/iX Internet Services (MPE/iX 6.0)

Chapter 8 133
DNS BIND/iX
Data Files
The CNAME records create aliases for existing hosts. These examples
illustrate a few common uses:
www IN CNAME maxx.maxx.net.
ftp IN CNAME maxx.maxx.net.
You can give a host any alias you like, and as many aliases as you want.
The host needn’t answer to that name, that is, the alias doesn’t need to
be the host’s true name as reported by hostname or uname.
The other vital type of record is MX. This tells SMTP e-mail software
where to send mail for each named host:
lucy IN MX 10 lucy.maxx.net.
When a remote host’s mail delivery program sees an e-mail address in
your domain, it will query your name server for its applicable MX record
or records. Every user on your LAN can receive e-mail, even if not every
host is running its own e-mail software. The MX record for lucy, for
instance, could easily redirect e-mail to another host on the LAN.
The number (10 in this case) in the fourth field represents a preference
value. If you define multiple MX records for a host, delivery is attempted
to lower-preference value hosts first. The actual value isn’t important,
only its relationship to other preference values.
On larger LANs it’s a good idea to create backup e-mail servers.
Smaller LANs can simply rely on the fact that most SMTP mailers will
retry deliveries to the site for three days before returning a message to
its sender.
The line, shown commented out here, would arrange to redirect e-mail
for all hosts in this domain to a single machine:
;
; All mail for net delivered to nova
;
;* IN MX 10 nova.maxx.net.
This is a very good idea for LANs that benefit from a central e-mail
repository.
Address-to-Name Mapping
Also called reverse mapping, the zone.ADDR db file allows resolvers to
post queries armed with only the IP address of a host. This reverse
mapping is used, for example, by Internet server software that prefers
to log host names rather than less informative IP addresses.
Address-to-name mapping data will be provided for a DNS server by
PTR entries in its zone.ADDR files, one for every network served by
this DNS server, and its zone.LOCAL file.