??? For example, a wildcard mask
of 0.0.0.0 indicates a match of all 32 bits in the address.
area-id The area that is to be associated with the OSPF address range. It can be speci?¬?ed
either as a decimal value or in dotted-decimal notation, like an IP address.
A C B
172.16.1.1
172.16.1.0 192.168.1.0
10.1.1.1 10.1.1.2 10.2.2.2 10.2.2.3 192.168.1.1
S2 S2 S3 S3 E0 E0
Area = 0
146 Chapter 4: Single-Area OSPF Implementation
going to be published with the network area command, using a private IP address will save on
registered IP address space. Note that a loopback address requires a different subnet for each
router, unless the host address is advertised.
Using an address that is not advertised saves real IP address space, but unlike an address that is
advertised, the unadvertised address does not appear in the OSPF table and thus cannot be
accessed across the network. Therefore, using a private IP address represents a trade-off between
the ease of debugging the network and conservation of address space. Figure 4-5 highlights some
of the advantages and disadvantages of using advertised and unadvertised loopback addresses.
Figure 4-5 Loopback Addresses
Verifying the OSPF Con?¬?guration
You can use any one of a number of show commands to display information about an OSPF
con?¬?guration.
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