Source routing

IBM Token-Ring networking allows you to establish connections from your machine to other machines in these ways:

on a local ring

A local ring is the Token-Ring physically attached to your machine.

to other rings using gateways

A TCP/IP gateway is created when you configure TCP/IP over more than one Token-Ring adapter on the same machine. Those adapters must be connected to different rings and have different IP subnet addresses. TCP/IP gateways connected to Token-Ring networks in this manner will route TCP/IP traffic to the rings without using Token-Ring source routing. Similar gateways can be set up using the OSI protocol.

to other networks using a Token-Ring bridge

A Token-Ring bridge is a dedicated piece of computer hardware connected to several Token-Rings. The bridge routes frames between the rings. All Token-Rings connected via bridges will appear as a single ring to each station on the network. Token-Ring source routing allows your adapter to route network traffic across Token-Ring bridges regardless of the protocol stack used by any of the connected networks.

If you intend to connect your machine to a network that includes a bridge, and if you intend to send information from your machine across the bridge, you must use automatic Token-Ring source routing.

The Network Configuration Manager offers you two source routing options:

none

Source routing is not enabled; frames are not routed beyond the local ring.

auto

Source routing is enabled; frames include source routing information and the DLPI module performs source routing on behalf of the protocol stack. This is the default setting.

These options take effect for all protocol stacks using the specified adapter. It is possible for stacks to override default source routing without affecting the source routing mode used by other stacks. In such cases, the source routing is said to be in ``stack'' mode for the specific protocol stack. For example, TCP/IP can be configured to use automatic source routing of a Token-Ring or FDDI adapter, while a third-party SNA product can provide stack mode routing when using the same adapter.

Protocol stacks provide stack mode routing if the characteristics of the protocol prevent it from working with the general purpose source routing facility, or if a more specialized source routing that is designed to work optimally for a particular protocol is desired. Although no protocol stacks currently provide stack mode source routing, third-party networking products might contain such functionality.