3Com 5500-SI Configuration Manual page 246

246 C 16: IP R
HAPTER OUTING
P O
ROTOCOL PERATION
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 type-7 LSA route can be generated only if
the default route 0.0.0.0 is in the routing table.
Executing the
no-import-route
that OSPF imported through the
NSSA. Generally, if an NSSA router is both ASBR and ABR, this argument is used.
The command is used on the ABR attached to the NSSA. Using this
default-cost
command, you can configure the default route cost on the ABR to NSSA.
By default, the NSSA is not configured, and the cost of the default route to the NSSA
is 1.
Configuring the Route Summarization of OSPF Area
Route summary means that ABR can aggregate information of routes of the same
prefix and advertise only one route to other areas. An area can be configured with
multiple aggregate segments allowing OSPF can summarize them. When the ABR
transmits routing information to other areas, it will generate Sum_net_Lsa (type-3
LSA) per network. If continuous networks exist in this area, you can use the
command to summarize these segments into one segment. Thus, the
abr-summary
ABR only needs to send an aggregate LSA, and all the LSAs in the range of the
aggregate segment specified by the command are not transmitted separately.
Once the aggregate segment of a certain network is added to the area, all the
internal routes of the IP addresses in the range of the aggregate segment will no
longer be separately advertised to other areas. Only the route summary of the whole
aggregate network will be advertised. But if the range of the segment is restricted by
the parameter
not-advertise
This segment is represented by IP address and mask.
Route summarization can take effect only when it is configured on ABRs.
Perform the following configuration in OSPF Area View.
Table 236 C onfiguring the route summarization of OSPF area
Operation
Configure the Route Summarization
of OSPF Area
Cancel the route summarization of
OSPF Area
By default, the inter-area routes will not be summarized.
Configuring Summarization of Imported Routes by OSPF
Perform the following configurations in OSPF View.
Table 237 Configuring summarization of imported routes by OSPF
Operation
Configure summarization of
imported routes by OSPF
Remove summarization of
routes imported into OSPF
By default, summarization of imported routes is disabled.
command on the ASBR prevents the external routes
command from advertising to the
import-route
, the route summary of this segment is not advertised.
Command
abr-summary ip_address mask [ advertise |
not-advertise ]
undo abr-summary ip_address mask
Command
asbr-summary ip_address mask [ not-advertise |
tag value ]
undo asbr-summary ip_address mask