Major Features Of Cost-Based Automatic Routing Management - Cisco BPX 8620 Installation And Configuration Manual

Switch Software Description

Major Features of Cost-Based Automatic Routing Management

The following are major functional elements of Cost-Based Route Selection:
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Cisco BPX 8600 Series Installation and Configuration
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Enabling Cost-Based Route Selection—Enables cost-based route selection at any time and does not
require special password access. The default algorithm is the hop-based algorithm.
Configuring Trunk Cost—Assigns a trunk cost to each trunk, such as 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 is changed before or after the trunk is 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. Large-scale simultaneous network-wide
rerouting is avoided and gives you control over the connection reroute outage.
Cache vs. On-Demand Routing—Specifies that Hop-Based Route Selection always requires
on-demand routing in previous releases. 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.
The 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.
Enabling cost-based route selection automatically enables cache usage. Enabling Hop-Based Route
Selection automatically disables cache usage. Cache usage can also be independently enabled or
disabled for both types of route selection.
On-Demand Lowest Cost Route Determination—Specifies that on-demand routing selects the
current lowest cost route to the destination node. This lowest cost route is bounded by the maximum
route length of 10 hops. If more than one route of similar cost and distance is available, the route
with most available resources is chosen. No route grooming occurs after the initial routing. A
connection does not automatically reroute if the route cost changes over time. A connection also
does not automatically reroute if a lower cost route becomes available after the initial routing.
However, a forced reroute or a preferred route can be used to move the connection to a lower cost
route.
Delay-Sensitive Routes—Specifies that the delay-sensitive IGX connection types, such as voice and
nontimestamped data is configured to use the worst case queueing delay per trunk, rather than the
configured trunk cost, in the lowest-cost route determination. The trunk delay acts as the cost
attribute in the Dijkstra algorithm. The default mode for the delay sensitive connections is to use the
trunk cost. All other connection types always use the trunk cost in the route determination.
Automatic Routing Management does not use the worst case end-to-end queueing delay in route
selection for delay sensitive BPX connection types (ATM CBR). Cost-based route selection does not
change this.
Cost Cap—Determines a maximum allowable cost value, such as cost cap that is used during route
determination to prevent selection of a route, which exceeds an acceptable cost. For routing based
on delay, the cost cap is the acceptable end-to-end delay for the connection type. This cap is
configured network-wide per delay sensitive connection type.
For routing based on trunk cost, the cost cap is the acceptable end-to-end cost. This cap is configured
per connection. The default cost cap is 100, which is derived from the maximum hops per route (10)
and default cost per trunk (10). You can change the cost cap at any time. If the cost cap is decreased
Chapter 1 The BPX Switch: Functional Overview
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005