Configuring ranges on an ABR to reduce advertising to the backbone

Syntax:


area [[ospf-area-id] | [backbone]] range [[ip-addr/mask-length]] [no-advertise] [type summary [[cost 1-16777215] | [nssa] | [cost 1-16777215]]]


area ospf-area-id range ip-addr/mask-length [no-advertise] [type summary [[cost 1-16777215] | nssa]]

Use this command on a routing switch intended to operate as an ABR for the specified area to do either of the following:

Simultaneously create the area and corresponding range setting for routes to summarize or block.
For an existing area, specify a range setting for routes to summarize or block.

Options


ospf-area-id

Same area ID as in Configuring an OSPF backbone or normal area, except you cannot assign a backbone area number ( 0 or 0.0.0.0) to a stub or NSSA area.


range ip-addr/mask-length

Defines the range of route advertisements to either summarize for injection into the backbone area or to prevent from being injected into the backbone area. The ip-addr value specifies the IP address portion of the range, and mask-length specifies the leftmost significant bits in the address. The ABR for the specified area compares the IP address of each outbound route advertisement with the address and significant bits in the mask to determine which routes to select for either summarizing or blocking. For example, a range of 10.10.32.1/14 specifies all routes in the range of 10.10.32.1 - 10.10.35.254.


no advertise

Use this keyword only if you want to configure the ABR to prevent advertisement to the backbone of a specified range of routes. (This has the effect of "hiding" the specified range from the backbone area.) If you do not use this option, the ABR advertises the specified range of routes according to the type summary | nssa selection described below.


[type summary [[cost 1-16777215] | nssa]]

Configures the type of route summaries to advertise or block.

If the option type is not used in the command, the ABR defaults this setting to summary.

The option type summary [cost 1-16777215] specifies internal routes in the configured range of RAs and the user-configured cost for an area summary range. If cost is specified, the range will advertise the specified cost instead of the calculated cost.

If no advertise is used in the command, the ABR prevents the selected internal routes from being summarized in a type-3 LSA and advertised to the backbone.

If no-advertise is not used in the command, the selected routes are summarized to the backbone in a type-3 LSA.

Option nssa specifies external routes (type-7 LSAs) in the configured range of route advertisements. If no-advertise (above) is used in the command, the ABR prevents the selected external routes from being summarized in a type-5 LSA and advertised to the backbone. (Configure this option where an ABR for an NSSA advertises external routes that you do not want propagated to the backbone.)

If no-advertise is not used in the command, the selected routes learned from type-7 LSAs in the area are summarized to the backbone in a type-5 LSA.[cost 1-16777215]User configured cost for an NSSA summary range. If cost is not configured, the ABR will use the algorithm defined in RFC 3101 to compute the cost and metric-type of the summarized route. If cost is specified, then the range will advertise the specified cost as the cost of the summarized route.