Discussion

Chapter 7
CHAPTER 7
Router Interfaces7
7.0 Introduction
JUNOS routers have three types of interfaces: network, services, and special interfaces.
As you might expect, network interfaces physically connect to the network and
carry network traffic. Services interfaces manipulate the traffic before transmitting or
receiving it, for example, to perform Network Address Translation (NAT), IPSec
functions, or monitoring traffic flows. Special interfaces include two internal Ethernet
management interfaces and the loopback interface, which is not used for performance
monitoring but as a place to define an IP address for the router as a whole.
The naming conventions for the three types of interfaces are the same, and you configure
them the same way.
For interfaces to work, you must configure them. Simply installing the hardware in
the router is not sufficient. The router detects that network hardware is present and
you can list the hardware and interfaces with the show chassis hardware and show
interfaces terse commands, but they will not carry traffic. You can also configure
interfaces that are not present in the router, which is a handy feature when you are
preparing to receive new hardware or to move a Flexible PIC Concentrator (FPC) or
a Physical Interface Card (PIC) to another slot. When checking the configuration
during a commit operation, MGD, the management process (daemon), checks
whether the hardware corresponding to the configuration is present in the router. If it
is, MGD hands that portion of the configuration over to the proper processes for activation.
If the hardware is not present, MGD ignores that portion of the configuration.
When configuring interfaces on the router, you identify the interface by media type
and location in the router. The media type is a string, typically two letters, that identifies
the network device. Table 7-1 lists some of the common interface media names.
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