Reserved TCP/IP ports

With the netstat command (TSO or z/OS® UNIX) you can get an overview of the ports currently in use. The output of this command will look similar to the following example. The ports used are the last number (behind the "..") in the "Local Socket" column. Since these ports are already in use, they cannot be used for the z/OS Explorer configuration.

IPv4

MVS TCP/IP NETSTAT CS VxRy       TCPIP Name: TCPIP           16:36:42
User Id  Conn     Local Socket           Foreign Socket         State
-------  ----     ------------           --------------         -----
RSED     0000004B 0.0.0.0..4035          0.0.0.0..0             Listen
JMON     00000038 0.0.0.0..6715          0.0.0.0..0             Listen

IPv6

MVS TCP/IP NETSTAT CS VxRy       TCPIP Name: TCPIP           12:46:25
User Id  Conn     State
-------  ----     -----
RSED     0000004B Listen
  Local Socket:   0.0.0.0..4035
  Foreign Socket: 0.0.0.0..0
JMON     00000037 Listen
  Local Socket:   0.0.0.0..6715
  Foreign Socket: 0.0.0.0..0

Another limitation that can exist is reserved TCP/IP ports. There are the following two common places to reserve TCP/IP ports:

PROFILE.TCPIP
This is the data set referred to by the PROFILE DD statement of the TCP/IP started task, often named SYS1.TCPPARMS(TCPPROF).
- PORT: Reserves a port for specified job names.
- PORTRANGE: Reserves a range of ports for specified job names.
Refer to Communications Server: IP Configuration Guide (SC31-8775) for more information on these statements.
SYS1.PARMLIB(BPXPRMxx)
- INADDRANYPORT: Specifies the starting port number for the range of port numbers that the system reserves for use with PORT 0, INADDR_ANY binds. This value is only needed for CINET (multiple TCP/IP stacks active on a single host).
- INADDRANYCOUNT: Specifies the number of ports that the system reserves, starting with the port number specified in the INADDRANYPORT parameter. This value is only needed for CINET (multiple TCP/IP stacks active on a single host).
Refer to UNIX System Services Planning (GA22-7800) and MVS Initialization and Tuning Reference (SA22-7592) for more information on these statements.

These reserved ports can be listed with the netstat portl command (TSO or z/OS UNIX), which creates an output like that in the example as follows:

MVS TCP/IP NETSTAT CS VxRy       TCPIP Name: TCPIP           17:08:32
Port# Prot User     Flags    Range       IP Address
----- ---- ----     -----    -----       ----------
00007 TCP  MISCSERV DA
00009 TCP  MISCSERV DA
00019 TCP  MISCSERV DA
00020 TCP  OMVS     D
00021 TCP  FTPD1    DA
00025 TCP  SMTP     DA
00053 TCP  NAMESRV  DA
00080 TCP  OMVS     DA
03500 TCP  OMVS     DAR      03500-03519
03501 TCP  OMVS     DAR      03500-03519

Refer to Communications Server: IP System Administrator’s Commands (SC31-8781) for more information on the NETSTAT command.

Note: The NETSTAT command only shows the information defined in PROFILE.TCPIP, which should overlap the BPXPRMxx definitions. In case of doubt or problems, check the BPXPRMxx parmlib member to verify the ports being reserved here.