TITLE
    Open Transport 1.3: Single Link Multi-homing Setup
Article ID:
Created:
Modified: 		30337
1/13/98
3/14/00
TOPIC

    Open Transport 1.3 introduces Single Link Multi-homing, a mechanism by which Open Transport can support multiple IP addresses on the same hardware interface, at the same time.

    Synonyms for this feature include IP Aliasing, Secondary IP address Support, IP Masquerading, "Multihoming", IP Multinode support.

    This is useful for sites like Internet Service Providers (ISPs), that want to give each of their clients a distinct IP address, without requiring separate computers for each address. Web server software packages, or server plug-ins that utilize this feature can offer virtual domain support that supports all web browsers.

    You will need to contact your application developer to see if they are supporting this new feature of Open Transport. This feature is only available with Open Transport 1.3 and later.

DISCUSSION

    You configure a system to use multiple IP addresses as follows:

    1. The TCP/IP Control Panel must be set for manual addressing.

    2. You create a text file with the required name "IP Secondary Addresses" and put it into the Preferences folder in the System Folder.

    Each line of the IP Secondary Addresses file contains a secondary IP address to be used by the system, and an optional subnet mask and router address for the secondary IP address. If there is no subnet mask entry, then a default subnet mask for the IP address class will be used. If there is no router address entry, then the default router associated with the primary address will be used.

    Each secondary address entry must be prefixed by "ip=". Each subnet mask entry must be prefixed by "sm=". Each router address entry must be prefixed by "rt=". Lines proceeded by a ; are ignored. An example of the contents of the IP Secondary Addresses file follows.

    'ip=' for ip address, 'sm=' subnet mask, 'rt=' router address. There should be no commas in this line as shown between entries.

    Note: No space in 'ip=192.168.22.200'
    IP address
    Subnet Mask
    Router addresses
    ip=192.168.22.200
    sm=255.255.255.0
    rt=192.168.20.1
    ip=192.168.22.201
    -
    rt=192.168.20.1
    ip=192.168.22.202
    -
    -


    The order of the entries is important. The "rt=" entry must follow the "sm=" entry if used.

    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.

    When Open Transport binds a TCP/IP connection, if there is an address conflict with 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 computer 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 computers, reconfigure TCP/IP on one of the computers so there is no longer an address conflict, then relaunch your TCP/IP applications.

Document Information
Product Area: Communications-Networking
Category: Open Transport
Sub Category: General Topics

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