OSPF range cost
Assign a fixed cost to area summary routes, including routing instances.
Area border routers (ABRs) can advertise a summary route instead of individual routes that originate within an autonomous system (AS). This feature lets you specify a fixed cost to advertise along with the summary route.
If you do not specify a fixed cost then the cost of the summary route is equal to the maximum cost of all the individual routes that are in the summary route.
This feature applies to inter-AS summary routes that you configure with the
range and range keyword combination. It does not apply to external routes that are redistributed into OSPF.
Behavior with range cost configuration
Use of this feature entails an optional override of routing costs. When configured, the fixed cost overrides the calculated cost.
If you do not configure a cost for the summary route, then the cost is calculated automatically as the maximum cost of all the individual routes that are covered by the summary. If you do configure a cost, this overrides that automatic calculation.
Configuring a fixed cost metric for an area summary range is significant only when the range is advertised to peers. For example, if the range is configured as
not-advertise or if no path matches the range, it is not advertised.
The range's configuration can include the
not-advertise parameter. If
not-advertise is specified:
- No prefixes that match the range are advertised.
- The range itself is not advertised.
- Any configured cost for the range is meaningless and is ignored.
- If the
not-advertisecondition is subsequently removed, any fixed-cost configuration is applied.
- If no prefixes are matched in the range configuration, the range is not advertised.
- If one or more prefixes do match the range, the whole range is advertised instead of just the matching prefixes (unless the range is configured with
Any change in the cost configuration (adding a cost, removing the cost, or changing the cost value) causes OSPF to send the new cost in an update to its peers.