Junos® OS For Dummies®, 2nd Edition

Configuring the Management and Loopback Interfaces

The major characteristic of network devices is that they have network interfaces, and usually more than one. Routers can have literally hundreds and so can large switches.

The Junos OS supports many types of interfaces, including these:

• The Ethernet family (Fast Ethernet, Gigabit Ethernet, and so on)
• Serial interfaces
• Public transport interfaces, such as T1/E1, SONET/SDH, and others
• Public network interfaces, such as frame relay or ATM
• Multicast interfaces
• ADSL
• Tunnel interfaces
• Loopback interface (lo0)
• Management interface (fxp0)

This section looks at configuring the last two interface types on the list: the management interface (usually fxp0) and the loopback interface (lo0, short for “loopback 0”). Both of these interfaces, lo0 and fxp0, are critical to get right for correct device operation. But, first, take a look at the physical and logical properties that must be set for any interface.

Knowing the physical and logical interface properties

The first thing that pops into your mind when you think about interfaces is probably the IP address. IP addresses are assigned to individual interfaces, and those addresses are used by protocols and other routing features to control traffic within the router and within the network to which that router is connected.

However, nothing about an interface says that it must have a specific IP address assigned to it. In fact, you can assign the same address to an Ethernet interface and then ...