Assigning an area range (optional)
You can assign a range for an area, but it is not required. Ranges allow a specific IP address and mask to represent a range of IP
addresses within an area, so that only that reference range address is advertised to the network, instead of all the addresses within that
range. Each area can have up to 32 range addresses.
To define an area range for subnets on 10.45.5.1 and 10.45.6.2, enter the following command.
device(config)# router ospf
device(config-ospf-router)# area 10.45.5.1 range 10.45.0.0 255.255.0.0
device(config-ospf-router)# area 10.45.6.2 range 10.45.0.0 255.255.0.0
Syntax:
[no] area
{
num
|
ip-addr
}
range
ip-addr ip-mask
The
num
and
ip-addr
parameters specify the area number, which can be in IP address format.
The
range
ip-addr
parameter specifies the IP address portion of the range. The software compares the address with the significant bits in
the mask. All network addresses that match this comparison are summarized in a single route advertised by the router.
The
ip-mask
parameter specifies the portions of the IP address that a route must contain to be summarized in the summary route. In the
example above, all networks that begin with 10.45 are summarized into a single route.
Assigning an area cost (optional parameter)
You can assign a cost for an area, but it is not required. To consolidate and summarize routes at an area boundary, use the
area range
cost
command in router configuration mode.
If the
cost
parameter is specified, it will be used (overriding the computed cost) to generate the summary LSA. If the
cost
parameter is
not specified, then the existing range metric computation max or min cost of routes falling under this range will be used to generate
summary LSA.
NOTE
The area should be already configured before using this
command.
Creates an area range entry with ip address 10.1.1.1 and network mask 255.255.255.0 with the area-id 10.
device(config)# router ospf
device(config-ospf-router)# area 10 range 10.1.1.1 255.255.255.0
Modifies the address range status to
DoNotAdvertise
. Neither the individual intra-area routes falling under range nor the ranged prefix is
advertised as summary LSA.
device(config)# router ospf
device(config-ospf-router)# area 10 range 10.1.1.1 255.255.255.0 not-advertise
Modifies the address range status to advertise and a Type 3 summary link-state advertisement (LSA) can be generated for this address
range.
device(config)# router ospf
device(config-ospf-router)# area 10 range 10.1.1.1 255.255.255.0 advertise
Modifies the address range status to advertise and assign cost for this area range to 10.
device(config)# router ospf
device(config-ospf-router)# area 10 range 10.1.1.1 255.255.255.0 advertise cost 10
Modifies the address range status to not-advertise and cost from 10 to 5.
device(config)# router ospf
device(config-ospf-router)# area 10 range 10.1.1.1 255.255.255.0 not-advertise cost 5
Configuring OSPF
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