Microsoft Knowledge Base Article 230623 contains the following summary:
A standard Windows configuration functions as a single-route software
router.
This operation is in contrast to a multiple-route hardware
router that may also exist in some environments.
Sometimes administrators attempt to configure Windows to perform
like a multiple-route hardware
router,
but because Windows is not designed to do this,
these attempts do not succeed.
One key difference between Windows
routers and hardware
routers is that a standard Windows configuration maintains a single
route table for all kernel-level
routing decisions.
This means that when a WinSock call is made,
a single
route table is consulted to determine the best
route for all network traffic.
A hardware
router,
or multiple-route
router,
can usually be configured to maintain a
route table for each interface.
The ability to provide this type of functionality in a hardware
router usually
requires additional microprocessors to accommodate the added complexity of the
routing algorithms.
With this added processing power,
hardware
routers are able to maintain more than one
routing table for
routing decisions,
and are therefore considered multiple-route
routers.
A standard Windows configuration is a single-route
router by design.
This means that programmers may not be able to perform certain activities of which a multiple-route
router is capable.
