ShareWay IP Professional Edition
User's Guide

Appendix

 

Multiple IP Addresses With Mac OS 8.1

Open Transport, shipped with Mac OS 8.1, allows multiple IP addresses to be assigned to a single Macintosh. Synonyms for this feature include IP Aliasing, Secondary IP Address Support, IP Masquerading, "Multihoming", IP Multimode support.

To configure the ShareWay Macintosh to use multiple IP addresses:

  1. Set the TCP/IP Control Panel for manual addressing.
  2. Create a text file with the required name "IP Secondary Addresses" and put it into the Preferences folder. A sample "IP Secondary Addresses" file is included with ShareWay IP Professional.

Each line of the IP Secondary Addresses file contains a secondary IP address to be used by the system. Each line also has fields for an optional subnet mask and router address for its secondary IP address, but they are not relevant to ShareWay IP and will not be discussed here. If fields for the optional subnet mask and router address are missing, Open Transport will use a default subnet mask for each line's IP address class, and the default router associated with the primary address.

Thus, each line has the form:

ip=xxx.xxx.xxx.xxx

Lines proceeded by a ";" are ignored. For example,

; Note: no white space in any 'ip=' line
ip=192.168.22.200
ip=192.168.22.201
ip=192.168.22.202

When Open Transport activates TCP/IP, the primary address will be obtained from the TCP/IP Control Panel setting. Open Transport then looks for the "IP Secondary Addresses" file in the Preferences folder to determine if additional addresses should also be configured. If there are duplicate IP address entries in the IP Secondary Addresses file, the duplicate addresses will be ignored. If there is an address conflict between a ShareWay-assigned IP address and either the primary or any secondary addresses with another host, Open Transport will present an error message using a dialog box and unload Open Transport/TCP from memory. The error dialog will display the conflicting IP address, the hardware address of the conflicting machine and note that your TCP/IP network interface has been shut down.

To resolve the conflict, quit all of the TCP/IP applications on both conflicting machines, reconfigure TCP/IP on one of the machines so there is no longer an address conflict, then relaunch your TCP/IP applications.

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