Ephemeral ports

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As with many client/server models, once a client connection has been established with an RSCT subsystem daemon (such as an RMC daemon), the client communicates with the daemon on an ephemeral port in order for the daemon to accept new requests on its base port. Blocking ephemeral port ranges may cause an application that has established a connection with a daemon to fail.

Ephemeral port ranges vary by operating system. On AIX® nodes, the following command can be used to determine ephemeral port ranges: 
/usr/sbin/no -a | fgrep ephemeral
The following output is displayed:
tcp_ephemeral_low = 32768
tcp_ephemeral_high = 65535
udp_ephemeral_low = 32768
udp_ephemeral_high = 65535
On AIX nodes:
  • There is an ephemeral port range for TCP and one for UDP. They can overlap, or be the same range.
  • The low values cannot be set to anything less than 1024.
  • If a free port in the ephemeral range cannot be obtained, the bind or connect operation will report a failure back to the application.
On Linux® nodes, the following command can be used to determine ephemeral port ranges: 
cat /proc/sys/net/ipv4/ip_local_port_range
The following output is displayed:
32768   61000

The preceding AIX and Linux commands display operating system settings.

The range of allowable ephemeral port values might also be affected by applications that support ephemeral port customization. For example, a firewall application may allow ephemeral port ranges to be defined on a per-service basis.

RSCT uses the ephemeral port values supplied by the operating system.