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2.6 | ![]() |
IP Unnumbered | |
2.6.1 | ![]() |
Using IP unnumbered |
This module has presented several ways
to maximize the use of IP addresses in an organization. In previous
sections, it was learned that wasting an entire subnet on the
point-to-point serial links could be avoided by using VLSM, or use
private addresses instead. Neither technique can be supported by
classful routing protocols, such as the popular RIP v1 and IGRP.
Fortunately, the Cisco IOS offers a third option for efficiently
addressing serial links. This option is known as IP unnumbered. When a
serial interface is configured for IP unnumbered, it does not need its
own address. This is because it borrows the IP address of another
interface, usually a LAN interface or loopback interface.
The RTA E0, 168.71.5.1, and RTB E0, 168.71.8.1, can communicate using
TCP/IP over this serial link, even though they do not belong to the same
IP network.
There are certain drawbacks that come with using IP unnumbered:
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