Specifications

A
DNS — Domain Name Service
Line 9: The IN NS specifies the name server responsible for this do-
main. The same is true here that gateway is extended to gate-
way.world.cosmos because it does not end with a ‘.’. There can be
several lines like this, one for the primary and one for each secondary
name server. If notify is not set to no in /etc/named.conf, all the
name servers listed here will be informed of the changes made to the
zone data.
Line 10: The MX record specifies the mail server that accepts, processes, and
forwards e-mails for the domain world.cosmos. In this example, this is
the host sun.world.cosmos. The number in front of the host name is the
preference value. If there are multiple MX entries, the mail server with
the smallest value is taken first and, if mail delivery to this server fails,
an attempt will be made with the next higher value.
Line 12–17: These are now the actual address records where one or more
IP addresses are assigned to the host names. The names are listed here
without a ‘.’, because they are entered without a domain added and
can all be appended with world.cosmos. Two IP addresses are assigned
to the host gateway, because it has two network cards.
The pseudodomain in-addr.arpa is used to assist the reverse lookup of IP ad-
dresses into host names. This will be appended, for this purpose, to the net-
work components described here in reverse order. 192.168.1 is thus translated
into 1.168.192.in-addr.arpa. See File 14.
1. $TTL 2D
2. 1.168.192.in-addr.arpa. IN SOA gateway.world.cosmos.
root.world.cosmos. (
3. 2001040901 ; serial
4. 1D ; refresh
5. 2H ; retry
6. 1W ; expiry
7. 2D ) ; minimum
8.
9. IN NS gateway.world.cosmos.
10.
11. 1 IN PTR gateway.world.cosmos.
12. 2 IN PTR earth.world.cosmos.
13. 3 IN PTR mars.world.cosmos.
File 14: Reverse Lookup
165SuSE Linux – Firewall on CD2