Routed On-Demand Calls - Novell NETWARE 6-DOCUMENTATION Manual

Routed On-Demand Calls

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Internetwork Packet Exchange
With an on-demand call, the link remains inactive until user data needs to
cross it. Workstations needing to reach remote destinations send packets to
their local IPX router advertising the routes, assuming the packets can reach
their destination. The local router stores the packets and tries to establish a
connection to the remote router. After the local router completes the call and
negotiates on-demand service, it forwards the stored packets to the remote
router, which then forwards them to their destination.
NOTE:
To avoid activating potentially expensive connections, IPX routers do not
forward type 20 (NetBIOS) packets over on-demand calls.
For more information about on-demand calls, refer to "Understanding" in the
routing documentation for NetWare/Link PPP.
NetWare routing also enables you to configure a routed on-demand call.
Unlike the standard on-demand call, which relies on statically configured
routes and services, a routed on-demand call runs a routing protocol while the
link is active. When the link goes down, the routes and services made known
by the routing protocol become unavailable.
If no data crosses the link after some period of time, a Data-Link layer timer
triggers the termination of an on-demand call. However, the routing protocol
running over a routed on-demand call resets this timer each time it transmits a
packet. This keeps the link continuously active. To solve this problem, the
routing software uses a similar timer that operates at the Network layer. This
timer is reset only when data packets—not protocol packets—cross the link.
In this way, the routing updates do not keep the link active when no data is
being transmitted.
Routed on-demand calls are well-suited for large corporate networks that have
many branch offices. In this type of internetwork, most of the traffic is
unidirectional: from the branch office to the corporate network. Configuring
each branch office with a single (default) route to the corporate network is
sufficient. When a branch office router establishes a link to the router serving
the corporate network, the routing protocol floods the branch office routes into
the corporate network. This is necessary so that responses to branch office
service requests know how to reach their destination in the branch office
network. As long as the branch office forwards information to the corporate
network, the link remains active. If the link is idle for some predetermined
period of time, it goes down.