Network Address
AND
Subnet Mask
=
Network Address
Host Address
AND
Subnet Mask
=
Same Network
Address
Figure 15-11. Summarizing a Range of Networks
If necessary, you can specify more than one route summary for an area. For
example, you may want to specify more than one route summary if an area
includes non-contiguous subnets. Simply enter the area <area ID> range
command more than once, each time including the area ID and only the range
of network addresses to be included in the single summary.
A well-designed network greatly simplifies the configuration of areas. You will
find it easier to configure route summaries if the WAN is subdivided into
contiguous networks at each site. The IT staff at each site can then subdivide
these networks into the appropriate size and number of subnets.
By default, the ABR advertises summary routes as if the area is directly
connected. You can change this cost by entering this command from the OSPF
configuration mode context:
Syntax: area <area ID> default-cost <value>
The value sets the metric of the summary link that the ABR advertises to
routers in other areas and can be between 0 and 166,777,214. The default is 0.
IP Routing—Configuring RIP, OSPF, BGP, and PBR
192.168.1.0 255.255.192.0
11000000 10101000 00000001 00000000
11111111 11111111 11000000 00000000
10101000 00101101 00000000 00000000
192.168.0.0
192.168.63.0 255.255.192.0
11000000 10101000 00111111 00000000
11111111 11111111 11000000 00000000
10101000 00101101 00000000 00000000
192.168.0.0
Configuring OSPF
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