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@@ -200,7 +200,7 @@ When the
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option is specified, the servers used come from the
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.I dns
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attribute in the database. For example, to specify a set of dns servers that
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-systems on the network
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+will resolve requests for systems on the network
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.IR mh-net :
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.EX
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@@ -235,10 +235,11 @@ server names to their ip addresses. This is only
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a hint and will be superseded from whatever is learned
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from servers owning the domain.
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.PP
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-The root of a domain subtree served by the local database is indicated
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-by an entry with an
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-.B soa
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-attribute.
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+You can also serve a subtree of the domain name space from the local
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+database. You indicate subtrees that you'ld like to serve by
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+adding an
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+.B soa=
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+attribute to the root entry.
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For example, the Bell Labs CS research domain is:
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.EX
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@@ -266,6 +267,37 @@ and
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define the area refresh interval and the minimum TTL for
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records in this domain.
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.PP
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+You can also serve reverse lookups (returning the name that
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+goes with an IP address) by adding an
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+.B soa=
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+attribute to the entry defining the root of the reverse space.
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+For example, to provide reverse lookup for all addresses in
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+starting with 135.104 you must have a record like:
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+.EX
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+
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+dom=104.135.in-addr.arpa soa=
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+ refresh=3600 ttl=3600
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+ ns=plan9.bell-labs.com
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+ ns=ns1.cs.bell-labs.com
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+ ns=ns2.cs.bell-labs.com
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+.EE
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+Notice the form of the reverse address, i.e., it's the bytes of the
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+address range you are serving reversed and with
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+.B .in-addr.arpa
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+appended. This is a standard form for an IPv4 PTR record name.
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+.PP
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+If such an entry exists in the database, reverse addresses will
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+automaticly be generated from any IP addresses in the database
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+that are under this root. For example
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+.EX
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+
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+dom=ns1.cs.bell-labs.com ip=135.104.1.11
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+.EE
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+will automaticly create both forward and reverse entries for
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+.B ns1.cs.bell-labs.com .
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+Unlike other DNS servers, there's no way to generate
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+inconsistent forward and reverse entries.
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+.PP
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Delegation of a further subtree to another set of name servers
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is indicated by an
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.B soa=delegated
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