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.