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Top Forums UNIX for Advanced & Expert Users Let NTP listen only on one interface Post 302180793 by one71 on Tuesday 1st of April 2008 06:53:59 AM
Old 04-01-2008
Let NTP listen only on one interface

Hallo,

I have a machine which serves as NTP server. This machine has more (3) Network interfaces (+ loopback). By default NTP "binds" itself to all available interfaces, i.e. it listens on port 123 on all interfaces:

Code:
netstat -an|grep 123
udp        0      0  127.0.0.1.123          *.*
udp        0      0  1.2.3.4.123           *.*
udp        0      0  *.123                  *.*
udp        0      0  1.2.5.4.123           *.*
udp        0      0  1.2.6.4.123          *.*

I would like to "bind" NTP to only one interface, say the 1.2.3.4. Is it possible? I do not find any hint on the net.

Thanks.

p.s. I am interested in a solution for linux and HP-UX, in case of OS dependency.
 

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ntp.conf(5)							File Formats Manual						       ntp.conf(5)

Name
       ntp.conf - Network Time Protocol configuration file

Description
       The  file  is the configuration file for the Network Time Protocol (NTP) daemon, This file must be configured on your system before running
       Any host names that you specify in the file must have an entry in the file, or an entry in the master database, if the  database  is  being
       served to your system by BIND/Hesiod or Yellow Pages.

       The file has four entry formats:

       trusting no
	    This entry guarantees that your system synchronizes only to the NTP servers identified in the peer and server entries specified.  Dig-
	    ital recommends that all systems include the entry.

       peer server
	    This entry identifies server as one of the NTP servers that your system trusts, and from which your system will accept  time  synchro-
	    nization.	 Your  system  may  also  provide time synchronization to this server.	Servers can be identified by host name or internet
	    address.

	    NTP servers should be configured with entries.

       server server
	    This entry identifies server as one of the NTP servers that your system trusts, and from which your system will accept  time  synchro-
	    nization.	Your  system  can  not	provide  time  synchronization to this server.	Servers can be identified by host name or internet
	    address.

	    NTP clients should be configured with entries.

       peer   /dev/null       LOCL    1       -5      local
	    This entry identifies your system as a local reference clock.  A local reference clock is the most accurate system clock available	at
	    your  site.   If you receive time synchronization from the Internet NTP service, you should not include this entry on any of your sys-
	    tems.  At most, one system in a set of nodes running should be identified as a local reference clock.

	    A host which specifies this entry should not specify any or entries.

Examples
       This is a sample configuration file for an NTP client which receives time synchronization from the NTP servers: and Lines beginning with  a
       number sign (#) are comments.
       #
       #	       NTP  Configuration File
       #	This file is mandatory for the ntpd daemon
       #
       #
       #
       #   **  A L L  **
       #
       #  "trusting no" prevents this host from synchronizing
       #   to any host that is not listed below.  It is recommended
       #   that all hosts include the line "trusting no".
       #
       trusting no
       #
       #
       #    **	S E R V E R  **
       #
       #  If you are configuring a server, use "peer" entries to
       #  synchronize to other NTP servers.  For example, server1,
       #  server2, and server3.
       #
       #peer	      server1
       #peer	      server2
       #peer	      server3
       #
       #
       #
       #
       #    **	C L I E N T  **
       #
       #  If you are configuring a client, use "server" entries to
       #  synchronize to NTP servers.  For example, server1, server2,
       #  and server3.
       #
       server	      server1
       server	      server2
       server	      server3
       #
       #
       #
       #    **	L O C A L   R E F E R E N C E	C L O C K  **
       #
       #  If you are configuring a local reference clock, include the
       #  following entry and the "trusting no" entry ONLY.
       #
       #peer	 /dev/null LOCL 1    -5   local
       #

See Also
       ntp(1), ntpd(8), ntpdc(8)
       RFC 1129--Internet time synchronization:  The Network Time Protocol
       Introduction to Networking and Distributed System Services

																       ntp.conf(5)
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