JUNOS Enterprise Routing

Interface Properties

Each interface has two types of properties assigned to it: physical properties and logical properties. Physical properties are tied to the entire physical port, whereas logical properties affect only that logical portion of the interface represented by unit numbers or channel numbers.

Physical Properties

A physical property on an interface is any property that should be assigned to the entire physical port. Depending on the interface media, a large range of properties can be configured, but they can be divided into a few major categories:

Clocking

This aligns the bits as they are transmitted out of the interface. The clocking can be learned either from an external source or from the router itself.

Encapsulation

This is the Layer 2 encapsulation that is going to be used on the interface. Examples include Frame Relay, Point-to-Point Protocol (PPP), and Cisco High-Level Data Link Control (HDLC).

MTU

This is the maximum transmission unit, which is the maximum size of the frame transmitted from the interface.

Keepalives

These are mechanisms used to verify the operation of the interface. Most encapsulations have keepalives enabled by default, but you can disable them to aid in troubleshooting.

Layer 1/2 options

These are various bit and byte settings for the interface media. For a T1 interface, this includes byte encodings, framing, frame check sequences (FCSs), and line buildouts. In comparison, a Fast Ethernet interface might have options such as flow control, loopbacks, ...