
OSPF
115
By default, the STUB area is not configured, and the cost of the default route to a
STUB area is 1.
Configuring NSSA of OSPF
An NSSA is similar to a STUB area. However, NSSA does not allow importing
AS-External-LSAs (type-5 LSAs) although it does allow importing
NSSA-External-LSAs (type-7 LSAs). ASBRs can be configured to convert type-5
LSAs to type-7 LSAs to allow advertising of type-5 LSAs within the NSSA. Similarly,
ABRs can be configured to reconvert the type-7 LSAs to type-5 LSAs as these LSAs
leave the NSSA.
For example, in Figure 5, the AS running OSPF includes three areas: Area 1, Area 2
and Area 0. Among them, Area 0 is the backbone area. Also, there are other two
ASs running RIP. Area 1 is defined as an NSSA. After RIP routes of Area 1 are
propagated to the NSSA ASBR, the NSSA ASBR generates type-7 LSAs which are
propagated in Area 1. When the type-7 LSAs reach the NSSA ABR, the NSSA ABR
translates it into a type-5 LSA, which is propagated to Area 0 and Area 2. On the
other hand, RIP routes of the AS running RIP are translated into type-5 LSAs that
are propagated in the OSPF AS. However, the type-5 LSAs do not reach Area 1
because Area 1 is an NSSA. NSSAs and STUB areas have the same approach in this
aspect.
Similar to a STUB area, the NSSA cannot be configured with virtual links.
Figure 5
NSSA
Perform the following configuration in OSPF Area view.
All routers connected to the NSSA must use the
nssa
command to configure the
area with the NSSA attribute.
The
default-route-advertise
parameter is used to generate the default type-7
LSAs. The default type-7 LSA route is generated on the ABR, even though the
default route 0.0.0.0 is not in the routing table. On an ASBR, however, the default
Table 37
Configuring NSSA of OSPF
Operation
Command
Configure an area to be the NSSA area
nssa
[
default-route-advertise
] [
no-import-route
] [
no-summary
]
Cancel the configured NSSA
undo
nssa
Configure the default cost value of the route
to the NSSA
default-cost
cost
Restore the default cost value of the route to
the NSSA area
undo
default-cost
RIP
RIP
Area 2
Area 0
Area 1
NSSA
NSSA
ABR
NSSA
ASBR
Summary of Contents for Switch 7700
Page 10: ...2 ABOUT THIS GUIDE ...
Page 52: ...44 CHAPTER 2 PORT CONFIGURATION ...
Page 194: ...186 CHAPTER 5 IP ROUTING PROTOCOL OPERATION ...
Page 195: ...Route Capacity 187 ...
Page 196: ...188 CHAPTER 5 IP ROUTING PROTOCOL OPERATION ...
Page 197: ...Route Capacity 189 ...
Page 198: ...190 CHAPTER 5 IP ROUTING PROTOCOL OPERATION ...
Page 237: ...GMRP 229 SW7700 Ethernet1 0 1 gmrp ...
Page 238: ...230 CHAPTER 6 MULTICAST PROTOCOL ...
Page 270: ...262 CHAPTER 7 QOS OPERATION ...
Page 320: ...312 CHAPTER 9 AAA AND RADIUS OPERATION ...
Page 330: ...322 CHAPTER 10 RELIABILITY ...
Page 390: ...382 CHAPTER 11 SYSTEM MANAGEMENT ...