JUNOS Enterprise Routing

Permanent Interfaces

A permanent interface is any interface that is always present on the router (it cannot be altered). These interfaces can be management interfaces such as Ethernet, software pseudointerfaces such as tunnel interfaces, or fixed-port LAN/WAN interfaces.

On an M/T-series router, two management interfaces exist:

fxp0

This is an Out of Band (OOB) management Ethernet interface. It is connected to the router’s Routing Engine (RE) and can be used for Out of Band management access to the router. It can also be used to send management messages such as syslog or Simple Network Management Protocol (SNMP) traps. This interface is a nontransit interface, which means that traffic cannot enter this interface and exit via a LAN/WAN interface, nor can it enter a LAN/WAN interface and exit through the management interface.

Tip

When running routing protocols, be very careful when using the fxp0 interface. If you don’t configure the routing protocol correctly, you could have a route in your route table that points to the fxp0 interface and blackhole traffic, since this is a nontransit interface. To protect yourself from these types of situations, you should not run any routing protocols over this interface.

fxp1

This is an internal Fast Ethernet or Gigabit Ethernet (depending on the model of router) interface between the RE and the Packet Forwarding Engine (PFE). This interface is never configured but can be helpful when troubleshooting router issues. It is only in application-specific ...