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Reg port number 123 NTP

Super Advisor

Reg port number 123 NTP

Hi ,

We  have a nexus switch which is configured as ntp server.

when we are running from a client telnet 123 we are getting

telnet: connect: A remote host refused an attempted connect operation


Is it because of 123 being udp port ?

but my /etc/services show that its tcp port too .

Honored Contributor

Re: Reg port number 123 NTP



You can use xntpdc command to test connection to ntp server.


xntpdc is used to query the xntpd daemon about its current state and  to request changes in that state. The program may be run either in  interactive mode or controlled mode using command line arguments.
Extensive state and statistics information is available through the   xntpdc interface. In addition, nearly all the configuration options  which can be specified at start up using xntpd's configuration file  may also be specified at run time using xntpdc.  If one or more  request options is included on the command line when xntpdc is   executed, each of the requests will be sent to the NTP servers running   on each of the hosts given as command line arguments, or on localhost  by default. If no request options are given, xntpdc will attempt to
read commands from the standard input and execute these on the NTP  server running on the first host  given on the command line, again   defaulting to localhost when no other host is specified.  xntpdc will
prompt for commands if the standard input is a terminal device.


man xntpdc





Honored Contributor

Re: Reg port number 123 NTP

NTP works only on the UDP port.  So trying to telnet to port 123 will not work as telnet works over TCP.


Any port can be either TCP or UDP but /etc/services is purely for documentation purposes.  Just because it is in /etc/services does not mean it is usable.  The only way a port is available for use is if there is a program that opens it and listens for connections.