Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 466 — #492
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set to no in /etc/named.conf, all the name servers listed here are
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 exam-
ple, 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 deliv-
ery to this server fails, an attempt is made with the next higher value.
Lines 12–17: These are the actual address records where one or more IP
addresses are assigned to host names. The names are listed here with-
out a . because they do not include their domain, so world.cosmos
is added to all of them. Two IP addresses are assigned to the host
gateway, because it has two network cards. Wherever the host ad-
dress is a traditional one (IPv4), the record is marked with A. If the
address is an IPv6 address, the entry is marked with A6. (The previ-
ous token for IPv6 addresses was AAAA, which is now obsolete.)
Line 18: The alias www can be used to address mond (CNAME means canoni-
cal name).
The pseudodomain in-addr.arpa is used for the reverse lookup
of IP addresses into host names. It is appended to the network part
of the address in reverse notation. So 192.168.1 is resolved into
1.168.192.in-addr.arpa. See Example 21.16.
Example 21.16: Reverse Lookup
1
2 $TTL 2D
3 1.168.192.in-addr.arpa. IN SOA gateway.world.cosmos. root.world.cosmos. (
4 2003072441 ; serial
5 1D ; refresh
6 2H ; retry
7 1W ; expiry
8 2D ) ; minimum
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10 IN NS gateway.world.cosmos.
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12 1 IN PTR gateway.world.cosmos.
13 2 IN PTR earth.world.cosmos.
14 3 IN PTR mars.world.cosmos.
Line 1: $TTL defines the standard TTL that applies to all entries here.
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21.7. DNS — Domain Name System