142 CHAPTER 6: IP ROUTING PROTOCOL OPERATION
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, the route summary of this segment is
not advertised. 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.
By default, the inter-area routes will not be summarized.
Configuring Summarization of Imported Routes by OSPF
Perform the following configurations in OSPF View.
By default, summarization of imported routes is disabled.
After the summarization of imported routes is configured, if the local router is an
autonomous system border router (ASBR), this command summarizes the
imported Type-5 LSAs in the summary address range. When NSSA is configured,
this command will also summarize the imported Type-7 LSA in the summary
address range.
If the local router works as an area border router (ABR) and a router in the NSSA,
this command summarizes Type-5 LSAs translated from Type-7 LSAs. If the router
is not the router in the NSSA, this summarization is disabled.
Configuring OSPF Virtual Link
According to RFC2328, after the area division of OSPF, the backbone is established
with an area-id of 0.0.0.0. The OSPF routes between non-backbone areas are
updated with the help of the backbone area. OSPF stipulates that all the
non-backbone areas should maintain the connectivity with the backbone area,
and at least one interface on the ABR should fall into the area 0.0.0.0. If an area
does not have a direct physical link with the backbone area 0.0.0.0, a virtual link
must be created.
If physical connectivity cannot be ensured due to the network topology
restrictions, a virtual link can be used to meet the requirements of RFC2328. The
Table 146 Configuring the route summarization of OSPF area
Operation Command
Configure the Route Summarization
of OSPF Area
abr-summary
ip_address mask
[ advertise
| not-advertise ]
Cancel the route summarization of
OSPF Area
undo abr-summary
ip_address mask
Table 147 Configuring summarization of imported routes by OSPF
Operation Command
Configure summarization of
imported routes by OSPF
asbr-summary
ip_address mask
[ not-advertise
| tag
value
]
Remove summarization of
routes imported into OSPF
undo asbr-summary
ip_address mask
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