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$Id: nsupdate.8,v 1.4 2000/08/01 01:18:45 tale Exp $
.Dd Jun 30, 2000 .Dt NSUPDATE 8 .Os BIND9 9 .Sh NAME .Nm nsupdate .Nd Dynamic DNS update utility .Sh SYNOPSIS .Nm nsupdate .Op Fl d .Oo .Fl y Ar keyname:secret | .Fl k Ar keyfile .Oc .Op Fl v .Sh DESCRIPTION .Nm nsupdate is used to submit Dynamic DNS Update requests as defined in RFC2136 to a name server. This allows resource records to be added or removed from a zone without manually editing the zone file. A single update request could contain requests to add or remove more than one resource record.
p Zones that are under dynamic control via .Nm nsupdate or a DHCP server should not be edited by hand. Manual edits could conflict with dynamic updates or the name server's transaction log activities which keep the file copy of the zone consistent with its internal representation in the name server's memory.
p The names of resource records that are dynamically added or removed with .Nm nsupdate have to be in the same zone. Requests are sent to the zone's master server. This is identified by the MNAME field of the zone's SOA record.
p The .Fl d option makes .Nm nsupdate operate in debug mode. This provides tracing information about the update requests that are made and the replies received from the name server.
p Transaction signatures can be used to authenticate the Dynamic DNS updates. These use the TSIG resource record type described in RFC2845. The signatures rely on a shared secret that should only be known to .Nm nsupdate and the name server. Currently, the only supported encryption algorithm for TSIG is HMAC-MD5, which is defined in RFC 2104. Once other algorithms are defined for TSIG, applications will need to ensure they select the appropriate algorithm as well as the key when authenticating each other. For instance suitable .Dv key{} and .Dv server{} statements would be added to
a /etc/named.conf so that the name server can associate the appropriate secret key and algorithm with the IP address of the client application that will be using TSIG authentication. .Nm nsupdate does not read
a /etc/named.conf .
p .Nm nsupdate uses the .Fl y and .Fl k options to provide the shared secret needed to generate a TSIG record for authenticating Dynamic DNS update requests. These options are mutually exclusive. The .Fl k option gets .Nm nsupdate to read the shared secret from the file .Ar keyfile . When the .Fl y is used, a signature is generated from .Ar keyname:secret. .Ar keyname is the name of the key, and .Ar secret is a string comprising the shared secret, typically written in base-64 encoding. Use of the .Fl y option is discouraged because the shared secret is supplied as a command line argument in clear text. This may be visible in the output from .Xr ps 1 or in a history file maintained by the user's shell.
p By default .Nm nsupdate uses UDP to send update requests to the name server. The .Fl v option makes .Nm nsupdate use a TCP connection. This may be preferable when a batch of update requests are made. .Sh INPUT FORMAT .Nm nsupdate reads commands from its standard input. Each command is supplied on exactly one line of input. Some commands are for administrative purposes. The others are either update instructions or prerequisite checks on the contents of the zone. These checks set conditions that some name or set of resource records (RRset) either exists or is absent from the zone. These conditions must be met if the entire update request is to succeed. Updates will be rejected if the tests for the prerequisite conditions fail.
p Every update request consists of zero or more prerequisites and one or more updates. This allows a suitably authenticated update request to proceed if some specified resource records are present or missing from the zone. A blank input line causes the accumulated commands to be sent as one Dynamic DNS update request to the name server.
p The command formats and their meaning are as follows: l -ohang indent t Xo c server Va servername Op port .Xc Sends all dynamic update requests to the name server .Va servername . When no server statement is provided, .Nm nsupdate will send updates to the master server of the correct zone. The MNAME field of that zone's SOA record will identify the master server for that zone. .Va port is the port number on .Va servername where the dynamic update requests get sent. If no port number is specified, the default DNS port number of 53 is used. t Xo c zone Va zonename .Xc Specifies that all updates are to be made to the zone .Va zonename . .Nm nsupdate will determine the correct zone to update based on the rest of the input data if no .Va zone statement is provided. t Xo c prereq nxdomain Va domain-name .Xc Requires that no resource record of any type exists with name .Va domain-name . t Xo c prereq yxdomain Va domain-name .Xc Requires that .Va domain-name exists as at least one resource record of any type. t Xo c prereq nxrrset Va domain-name Op class .Va type .Xc Requires that no resource record exists of the specified .Va type , .Va class and .Va domain-name . If .Va class is omitted, IN (internet) is assumed. t Xo c prereq yxrrset .Va domain-name Op class .Va type Op data... .Xc This requires that a resource record of the specified type .Va type , .Va class and name .Va domain-name must exist. If .Va class is omitted, IN (internet) is assumed. If .Va data is supplied, it has to exactly match the corresponding RDATA for .Va name . .Va data is written in the standard text representation of the resource record's RDATA. t Xo c update delete .Va domain-name Op class .Va Op type Op data... .Xc Deletes any resource records named .Va domain-name . If .Va type and .Va data is provided, only matching resource records will be removed. The internet class is assumed if .Va class is not supplied. t Xo c update add .Va domain-name ttl Op class .Va type data.. .Xc Adds a new resource record with the specified .Va ttl , .Va class and .Va data . .El .Sh EXAMPLES The examples below show how .Nm nsupdate could be used to insert and delete resource records from the .Dv 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 .Dv example.com . d -literal -offset indent # nsupdate > update delete oldhost.example.com A > update add newhost.example.com 86400 A 172.16.1.1 > .Ed
p Any A records for .Dv oldhost.example.com are deleted. and an A record for .Dv newhost.example.com it IP address 172.16.1.1 is added. The newly-added record has a 1 day TTL (86400 seconds) d -literal -offset indent # nsupdate > prereq nxdomain nickname.example.com > update add nickname.example.com CNAME somehost.example.com > .Ed
p The prerequisite condition gets the name server to check that there are no resource records of any type for .Dv 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 RFC1034 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 RFC2535 to allow CNAMEs to have SIG, KEY and NXT records.)
p .Sh NAME SERVER PROCESSING
p When a successful update request is made, the BIND9 name server increments the serial number in the zone's SOA record. A transaction log file is written containing details of the resource records that have been added or removed. This allows the name server to roll forward to the current state of the zone if it is restarted before a fresh copy of the zone file is written out by the name server. XXXJR WHEN DOES IT DO THAT??? It then sends a NOTIFY message to the zone's slave servers to inform them that the zone's contents have changed. .Sh FILES l -tag -width K{name}.+157.+{random}.private -compact t Pa /etc/named.conf name server configuration file t Pa K{name}.+157.+{random}.key base-64 encoding of HMAC-MD5 key created by .Xr dnssec-keygen 8 . t Pa K{name}.+157.+{random}.private base-64 encoding of HMAC-MD5 key created by .Xr dnssec-keygen 8 . .El .Sh SEE ALSO .Xr RFC2136 , .Xr RFC2137 , .Xr RFC2104 , .Xr RFC2845 , .Xr RFC1034 , .Xr RFC2535 , .Xr named 8 , .Xr dnssec-keygen 8 . .Sh BUGS The .Fl D and .Fl M options are not documented apart from this self-referential paragraph. They provide additional debugging information which is primarily of interest to the BIND9 developers. These options might be changed or removed in future releases.