3Com 3C13636 Configuration Manual page 624

3Com Router 3000 Ethernet Family
Configuration Guide
Table 4-29 Configure NSSA area parameters of OSPF
Configure an area to be an NSSA area
Remove a configured NSSA area
Configure the cost for transmitting the
default route to NSSA area
Restore the default cost for transmitting
the default route to NSSA area
By default, the NSSA is not configured, and the cost of the default route to the NSSA is
1.
If the ASBR is also the ABR in NSSA, you are often not recommended to redistribute
AS external route information twice respectively as Type-5 LSAs and Type-7 LSAs.
Then you can select the no-import-route parameter to forbid AS external route
information being advertised to the NSSA as Type-7 LSAs.
Since the NSSA gets limited AS external route information, so the ABR in it need to
advertise a default route via the Type-7 LSAs to ensure correct forwarding of packets to
the networks outside the AS. The default route information from the NSSA ABR will not
be converted into Type-5 LSAs, while that from the NSSA ASBR will be converted.
The default-route-advertise parameter, which is only available for NSSA ASBR or
ABR, is used to generate Type-7 LSAs for the default route.
When using the parameter at NSSA ABR, you can generate Type-7 LSAs for the
default route no matter whether there exists the default route 0.0.0.0 in the routing
table.
When using the parameter at NSSA ASBR, you can generate Type-7 LSAs for the
default route only if there exists the default route 0.0.0.0 in the routing table.
The no-summary parameter is only available for the ABR in NSSA, as is the same as
in stub area. When the parameter is selected, the NSSA ABR advertises a default route
via the Summary-LSAs (Type-3) in the area, but no other Summary-LSAs to other
areas.
Note:
The default-route-advertise parameter generates AS external default route which is
advertised in the NSSA via the Type-7 LSAs.
The no-summary parameter generates inter-area default route which is advertised via
the Type-3 LSAs.
Operation
3Com Corporation
4-29
Chapter 4 OSPF Configuration
Command
nssa [ default-route-advertise
[ no-import-route ] [ no-summary ]
undo nssa
default-cost cost
undo default-cost
]