Reference Guide
Open Shortest Path First (OSPFv2 and OSPFv3) | 675
Loopback interfaces also assist in the OSPF process. OSPF will pick the highest interface address as the
router-id and a loopback interface address has a higher precedence than other interface addresses.
The following text gives an example of the
show ip ospf process-id interface command with a Loopback
interface.
FTOS#show ip ospf 1 int
GigabitEthernet 13/23 is up, line protocol is up
Internet Address 10.168.0.1/24, Area 0.0.0.1
Process ID 1, Router ID 10.168.253.2, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 1
Designated Router (ID) 10.168.253.5, Interface address 10.168.0.4
Backup Designated Router (ID) 192.168.253.3, Interface address 10.168.0.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Neighbor Count is 3, Adjacent neighbor count is 2
Adjacent with neighbor 10.168.253.5 (Designated Router)
Adjacent with neighbor 10.168.253.3 (Backup Designated Router)
Loopback 0 is up, line protocol is up
Internet Address 10.168.253.2/32, Area 0.0.0.1
Process ID 1, Router ID 10.168.253.2, Network Type LOOPBACK, Cost: 1
Loopback interface is treated as a stub Host.
Configure stub areas
OSPF supports different types of LSAs to help reduce the amount of router processing within the areas.
Type 5 LSAs are not flooded into stub areas; the Area Border Router (ABR) advertises a default route into
the stub area to which it is attached. Stub area routers use the default route to reach external destinations
To ensure connectivity in your OSPFv2 network, never configure the backbone area as a stub area.
Use these commands in the following sequence, starting in EXEC Privilege mode to configure a stub area.
Step Command Syntax Command Mode Usage
1
show ip ospf
process-id [
vrf
vrf
name]
database
database-summary
EXEC Privilege Review all areas after they were configured to determine
which areas are NOT receiving type 5 LSAs.
vrf name: Show only the OSPF information tied to the VRF
process.
2
configure
EXEC Privilege Enter the CONFIGURATION mode.
3
router ospf
process-id [vrf {vrf
name}]
CONFIGURATION Enter the ROUTER OSPF mode.
Process ID is the ID assigned when configuring OSPFv2
globally.
vrf name: Enter the VRF key word and instance name to tie
the OSPF instance to the VRF. All network commands under
this OSPF instance are subsequently tied to the VRF instance.