Priority levels range from 0 (highest) to 15 (lowest). To use priorities, start with zero for the highest priority linkset for a given route and increment by one for lower priority linksets for that route. There can be no gaps in the priority assigned for a given route, although equal priorities are allowed.
Use linkset priorities to ensure that the shortest path is taken by a message, when available. In the following illustration, messages destined for STP 1.1.0 use linkset 1 (when available) and not linkset 2, which would require an extra hop through STP 1.1.1. Messages to STP 1.1.1 use linkset 2, if available:
To ensure that linkset 1 is always chosen for messages to STP 1.1.0, if available, a higher priority is assigned to route 1 in linkset 1. The same is done for STP 1.1.1, route 2, and linkset 2. Linkset priorities are defined in the configuration file by placing a comma and the priority after a route number in the linkset definition.
Note: Route 1 (STP 1.1.0) is assigned priority zero in linkset 1 and priority 1 in linkset 2, indicating linkset 1 is higher priority than linkset 2 for messages destined for STP 1.1.0. Route 2 (STP 1.1.1) is assigned the reverse priorities. Routes 3 and 4 have no priorities assigned to them, indicating both linksets are of equal priority for reaching SP 1.1.200 and SP 1.1.201. When a priority is not specified, the default of zero (highest) is assigned. Therefore specifying 3,0 and 4,0 in both linksets has the same result as not specifying a priority level at all. They are configured as equal priority because no matter which linkset is chosen, a message to either 1.1.200 or 1.1.201 requires two hops.
The following configuration sample shows how to specify linkset priorities for the illustrated example:
#
# Routing Parameters
#
ROUTE 0
DPC 1.1.100 # this node
DIRECTION UP
END
#
ROUTE 1
DPC 1.1.0 # STP 1.1.0
END
#
ROUTE 2
DPC 1.1.1 # STP 1.1.1
END
#
ROUTE 3
DPC 1.1.200 # SP 1.1.200
ADJACENT_ROUTE FALSE # Route to non-adjacent SP 1.1.200
END
#
ROUTE 4
DPC 1.1.201 # STP 1.1.201
ADJACENT_ROUTE FALSE # Route to non-adjacent SP 1.1.201
END
#
# Link Set Parameters
#
LINK_SET_DESCRIPTOR 1
ADJACENT_DPC 1.1.0
ROUTE_NUMBER 1,0
ROUTE_NUMBER 2,1
ROUTE_NUMBER 3
ROUTE_NUMBER 4
END
LINK_SET_DESCRIPTOR 2
ADJACENT_DPC 1.1.1
ROUTE_NUMBER 1,1
ROUTE_NUMBER 2,0
ROUTE_NUMBER 3
ROUTE_NUMBER 4
END