Setting Up Default Routes; Setting Up An Unnumbered Interface - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - IP-IPV6-IGP CONFIGURATION GUIDE 2010-10-31 Configuration Manual

JunosE 11.3.x IP, IPv6, and IGP Configuration Guide

Setting Up Default Routes

Setting Up an Unnumbered Interface

ip unnumbered
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Use to configure an unnumbered IP interface.
This command enables IP processing on an interface without assigning an explicit IP
address to the interface.
You must specify an interface location, which is the identifier of another interface on
which the router has an assigned IP address. This interface cannot be another
unnumbered interface.
Example 1
host1(config-if)#ip unnumbered fastEthernet 3/0
Example 2
host1(config-if)#ip unnumbered loopback 10
Use the no version to disable IP processing on the interface.
See ip unnumbered
A router examines its routing table to find a path for each packet. If the router cannot
locate a route, it must discard the packet. You can set up a default route using the special
address: 0.0.0.0. If the router cannot locate a path to a destination network and a default
route is defined, the router forwards the packet to the default router. For example:
host1(config)#ip route 0.0.0.0 0.0.0.0 192.56.21.3
Default routes are typically used to reduce the size of the routing table. Routing is
simplified because the router can test for a few local networks or use the default route.
However, a disadvantage of default routes is the possible creation of multiple paths and
routing loops.
An unnumbered interface does not have an IP address assigned to it. Unnumbered
interfaces are often used in point-to-point connections where an IP address is not required.
Use to set up an unnumbered interface.
This command enables IP processing on an interface without assigning an explicit IP
address to the interface.
You supply an interface location, which is the type and number of another interface
on which the router has an assigned IP address. This interface cannot be another
unnumbered interface.
Example
host1(config-if)#ip unnumbered fastEthernet 0/0
Use the no version to disable IP processing on an interface.
See ip unnumbered
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