.
my $update = Net::DNS::Update->new(foo.com);
$update->push("pre", nxrrset("3.13.168.192.in-addr.arpa. PTR testhost.foo.com."));
$update->push("update", rr_add("$3.13.168.192.in-addr.arpa. 86400 IN PTR testhost.foo.com."));

my $res = Net::DNS::Resolver->new;
$res->nameservers(nameserver.foo.com);
my $reply = $res->send($update);
.