Dell PowerConnect B-FCXs, Configuration Manual

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PowerConnect B-Series FCX Configuration Guide 935
53-1002266-01
Configuring OSPF
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The stub <cost> parameter specifies an additional cost for using a route to or from this area and
can be from 1 through 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.
Assigning 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 142 shows an example of an OSPF network containing an NSSA.
FIGURE 142
OSPF network containing an NSSA
This example shows two routing domains, a RIP domain and an OSPF domain. The ASBR inside the
NSSA imports external routes from RIP into the NSSA as Type-7 LSAs, which the ASBR floods
throughout the NSSA.
RIP Dom a in
L a yer 3
Switch
L a yer 3
Switch
L a yer 3
Switch
NSSA Are a 1.1.1.1
Intern a l ASBR
OSPF ABR
OSPF Are a 0
B a ckbone