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Bind port to a particular IP address

BINDADDR is a parameter on JANUS DEFINE, which defines and sets characteristics of a Janus port.

This parameter specifies the IP address to which the port will be bound, if the host (machine) on which Model 204 is running supports multiple IP addresses. The IP address must be an IP address of the host. If BINDADDR is not specified, the port binds the port number for all IP addresses associated with the host; that is, it can be accessed via any IP address associated with the host.


BINDADDR address

Where: address is a string containing the host IP address. Address formats for IPV4 and (as of version 7.7 of Model 204) IPV6 are supported:

  • IPV4 addresses are 32-bit integers, commonly displayed as "dotted decimal" 8-bit groups. For example, the IP address X'C6F2F40D' is commonly displayed (and must be specified for address) as
  • IPV6 addresses are 128-bit integers, represented with eight, colon-separated, 16-bit (four hex-digit) groups, which may be abbreviated and represented with fewer groups. For example, fe80:0000:0000:0000:0200:0000:0300:0016 or fe80::200:0:300:16.

    For more information about the supported format, see Recommended representation as text.


  • This parameter only really makes sense on a host with more than one IP address. For example, if a host on which an Online is running has IP addresses and, a BINDADDR specification indicates that the port can only be reached through IP address
  • BINDADDR is especially useful for allowing a single mainframe host or even an Online to act as more than one web server without the inconvenience of having port numbers on URLs. This can be done because there can be multiple port 80's (the default web port number) on the host, each accessed by its indicated BINDADDR. The separate IP addresses could, in turn, be associated with different DNS host names, even though these separate names refer to the same underlying machine.
  • There is not likely to be much, if any, performance benefit to having multiple Janus ports with the same port number but different BINDADDR specifications in the same Online. However, there might certainly be some organizational advantages to running such a configuration.

Valid for all port types.

See also