Quick Reference Guide

PowerConnect B-Series TI24X Configuration Guide 669
53-1002269-02
Configuring OSPF
23
Syntax: area <num> | <ip-addr> stub <cost> [no-summary]
The <num> | <ip-addr> parameter specifies the area number, which can be a number or in IP
address format. If you specify a number, the number can be from 0 – 2,147,483,647.
The stub <cost> parameter specifies an additional cost for using a route to or from this area and
can be from 1 – 16777215. There is no default. Normal areas do not use the cost parameter.
The no-summary parameter applies only to stub areas and disables summary LSAs from being sent
into the area.
NOTE
You can assign one area on a router interface. For example, if the system or chassis module has 16
ports, 16 areas are supported on the chassis or module.
Assign a Not-So-Stubby Area (NSSA)
The OSPF Not So Stubby Area (NSSA) feature enables you to configure OSPF areas that provide the
benefits of stub areas, but that also are capable of importing external route information. OSPF
does not flood external routes from other areas into an NSSA, but does translate and flood route
information from the NSSA into other areas such as the backbone.
NSSAs are especially useful when you want to summarize Type-5 External LSAs (external routes)
before forwarding them into an OSPF area. The OSPF specification (RFC 2328) prohibits
summarization of Type-5 LSAs and requires OSPF to flood Type-5 LSAs throughout a routing
domain. When you configure an NSSA, you can specify an address range for aggregating the
external routes that the NSSA's ABR exports into other areas.
The Dell implementation of NSSA is based on RFC 1587.
Figure 109 shows an example of an OSPF network containing an NSSA.
FIGURE 109 OSPF network containing an NSSA
RIP Domain
Layer 3
Switch
Layer 3
Switch
Layer 3
Switch
NSSA Area 1.1.1.1
Internal ASBR
OSPF ABR
OSPF Area 0
Backbone