0.0.0 mask.
Figure 4-4 shows an example of a single-area OSPF con?¬?guration on Router B.
Figure 4-4 Single-Area OSPF
Loopback Interfaces
The OSPF router ID is used to uniquely identify each router in the OSPF network. By default, this
ID is selected by the operating system from the con?¬?gured IP addresses on the router. To modify
the OSPF router ID to use a loopback address, ?¬?rst de?¬?ne a loopback interface with the following
command:
RouterX(config)# iinntteerrffaaccee llooooppbbaacckk number
The highest IP address, used as the router ID by default, can be overridden by con?¬?guring an IP
address on a loopback interface. OSPF is more reliable if a loopback interface is con?¬?gured
because the interface is always active and cannot be in a down state like a ???real??? interface can. For
this reason, the loopback address should be used on all key routers. If the loopback address is
Table 4-1 network Command Parameters
router ospf
Command
Parameters Description
address The network, subnet, or interface address.
wildcard-mask The wildcard mask. This mask identi?¬?es the part of the IP address that is to be
matched, where 0 is a match and 1 is ???don??™t care.
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