Selecting UDP ports

Last published : Sep 11, 2026
When you select a UDP port, select an available 16-bit integer from the range that follows:
  • Use available ports in the private range 49152 to 65535
  • Do not use the following ports:
    • Ports from the range of well-known ports, 0 to 1023
    • Ports from the range of registered ports, 1024 to 49151
To check which ports are defined as defaults for a node, examine the file /etc/services. You should also use the netstat command to list the UDP ports currently in use. For example:
\# netstat -a | more
UDP
   Local Address         Remote Address     State
--------------------  -------------------  ------
      *.*Unbound*.32771                              Idle
      *.32776                              Idle*.32777                              Idle
      *.name                               Idle*.biff                               Idle
      *.talk                               Idle*.32779                              Idle
      .
      .
      .
      *.55098                               Idle*.syslog                              Idle
      *.58702                               Idle*.*                                   Unbound\# netstat -a |head -2;netstat -a | grep udp
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address Foreign Address (state)
udp4       0      0  *.daytime*.*udp4       0      0*.time        *.*udp4       0      0*.sunrpc      *.*udp4       0      0*.snmp        *.*udp4       0      0*.syslog      *.*
Look in the UDP section of the output; the UDP ports that are listed under Local Address are already in use. If a port is listed in the /etc/services file, its associated name is displayed rather than the port number in the output.