Configuring and Managing MPE/iX Internet Services (August 2002)

Chapter 8
DNS BIND/iX
Data Files
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36000 ; Refresh every 10 hours
3600 ; Retry after 1 hour
360000 ; Expire after 100 hours
36000 ; Minimum TTL is 10 hours )
The “serial” field was discussed earlier.
The remaining four fields specify various time intervals (all values in seconds) used by the secondary name
server:
Refresh The time interval that must elapse between each poll of the primary by the secondary name
server (here 36,000 seconds or 10 hours). If the “serial number” has been updated on the
primary, the secondary assumes its data is stale and requests updated information as a
“zone transfer.”
Retry The time interval used between successive connection attempts by the secondary to reach
the primary name server in case the first attempt failed (here 3,600 seconds or one hour).
Generally, less than the “refresh” time.
Expire The time interval after which the secondary expires its data if it can’t reach the primary
name server (here 360,000 seconds or 100 hours). The secondary will refuse to service
requests after this interval.
Minimum The minimum time-to-live value, which specifies how long other servers should cache data
from the name server (here 36,000 seconds or 10 hours).
There are several types of resource records, identified by the key word in field three of each record. You may
present records in any order, but try to organize them for clarity. The NS (name server) record tells the hosts
that query your server where the name servers for this domain can be found:
maxx.net. IN NS nova.maxx.net.
You must include in this list at least one name server, that is the name of the server specified in the SOA
record. You can list multiple name servers for your domain. In fact, your domain should have at least two
name servers. Your Internet service provider will probably allow you to use their name server as a secondary
for your domain, but it must have the trailing dots!
maxx.net IN A 204.251.17.241
The first A record, which resolves a fully-qualified host name to an IP address, is a special one. It defines an
IP address for unqualified queries, that is, queries for the host maxx.net.
Other A records like this one:
lucy IN A 204.251.17.242
provide name-to-address mapping for a specific named host. The domain defined in this file (maxx.net) is
appended to the host name you show in the first field.
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.