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CCIE #29033
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How do you correctly advertise the loopback interface into OSPF using the correct mask?
Interface loopback address is 1.0.0.1/24
3 comments:
Loopback interfaces are advertised in OSPF as host routes (Stub routes). So 1.0.0.1/24 advertised with network statement 1.0.0.0 0.0.0.255 will show up in the routing table as 1.0.0.0/32 and not 1.0.0.0/24. To ensure the route is advertised with the correct mask use the following command under the interface loopback.
Example
interface loopback 0
ip address 1.0.0.1 255.255.255.0
ip ospf network point-to-point
"ip ospf network point-to-point" tells the interface to use a point-to-point network type removing the limitation of network type loopback.
The loopback will show up in the routing table as 1.0.0.1/32 not 1.0.0.0/32 (typing to fast) :P
I found a couple of other ways to ensure the loopback gets advertised with the right mask
router ospf 1
redistribute connected
or
Summarization using the "area range" command
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