Cost-Based Connection Routing; Major Features Of Cost-Based Autoroute - Cisco BPX-BXM-155-8DX Installation And Configuration Manual

Switch Software Description
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Routing group
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Cost-Based Connection Routing

In standard AutoRoute, the path with the fewest number of hops to the destination node is chosen as the
best route. Cost-based route selection uses an administrative trunk cost routing metric. The path with
the lowest total trunk cost is chosen as the best route.
Cost-based route selection is based on Dijkstra's Shortest Path Algorithm, which is widely used in
network routing environments. You can use cost-based route selection (that is, cost-based AutoRoute)
to give preference to slower privately owned trunks over faster public trunks that charge based on usage
time. This gives network operators more control over the usability of their network trunks, while
providing a more standard algorithm for route selection.

Major Features of Cost-Based AutoRoute

Here is a short description of the major functional elements of Cost-Based Route Selection.
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Cisco BPX 8600 Series Installation and Configuration
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Routing Group Configuration Example (continued)
Connection cell loading
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140 and up
Enabling Cost-Based Route Selection.
You enable cost-based route selection at any time. This feature does not require special password
access. The default algorithm is the hop-based algorithm.
Configuring Trunk Cost
You assign a trunk cost to each trunk (physical and virtual) in the network. One cost is assigned per
trunk; no separate costs are used for different connection or service types. The valid range of trunk
costs is 1 (lowest cost) to 50 (highest cost). A trunk has a default cost of 10 upon activation. The
cost of a trunk can be changed before or after the trunk has been added to the network topology.
The cost can also be changed after connections have been routed over the trunk. Such a change does
not initiate automatic connection rerouting, nor does it cause any outage to the routed connections.
If the new trunk cost causes the allowable route cost for any connections to be exceeded, the
connections must be manually rerouted to avoid the trunk. This avoids large-scale simultaneous
network-wide rerouting and gives you control over the connection reroute outage.
Cache vs. On-Demand Routing
In previous releases, Hop-Based Route Selection always requires on-demand routing. On-demand
routing initiates an end-to-end route search for every connection. Due to the computation time
required for Dijkstra's algorithm in cost-based route selection, a route cache is used to reduce the
need for on-demand routing.
This cache contains lowest cost routes as they are selected. Subsequent routing cycles use these
existing routes if the routing criteria are met. Otherwise on-demand routing is initiated. This
caching greatly benefits environments where routing criteria is very similar among connections.
Chapter 1 The BPX Switch: Functional Overview
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001