The examples below show how
nsupdate with BIND
9 could be used to insert and delete resource records from the example.com
zone. Notice that the input in each example contains a trailing blank
line so that a group of commands are sent as one dynamic update request
to the master name server for example.com.
# nsupdate
> update delete oldhost.example.com A
> update add newhost.example.com 86400 A 172.16.1.1
>
Any A records for oldhost.example.com are deleted,
and an A record for newhost.example.com at IP address 172.16.1.1
is added. The newly added record has a 1-day TTL (86400 seconds).
# nsupdate
> prereq nxdomain nickname.example.com
> update add nickname.example.com CNAME somehost.example.com
>
The prerequisite condition gets the name server to check
that there are no resource records of any type for nickname.example.com.
If there are, the update request fails. If this name does not exist,
a CNAME for it is added. This ensures that when the CNAME is added,
it cannot conflict with the long-standing rule in RFC 1034 that a
name must not exist as any other record type if it exists as a CNAME.
(The rule has been updated for DNSSEC in RFC 2535 to allow CNAMEs
to have SIG, KEY and NXT records.)