Interfaces

The term interfaces is used in a very specific way in this documentation. Interfaces are both physical and logical channels on the system that define how data is transmitted to and received from lower layers in the protocol stack. Conceptually, you configure an interface as part of the physical layer, layer 1.

You configure the physical and logical characteristics of T3 and T1 lines coming directly from your customer's premises or from a central office switch and OC3 lines going out to the core of your network infrastructure. These physical and logical characteristics define an interface.

Interface layering must always be configured in order from the lowest layer to the highest layer. For example, if you have already configured IP to run over ATM and you want to reconfigure the interface to run IP over PPP over ATM, you must first remove the IP interface, apply PPP, and then reapply IP.

Subinterfaces

A subinterface is a mechanism that allows a single physical interface to support multiple logical interfaces or networks. Several logical interfaces or networks can be associated with a single physical interface. Configuring multiple virtual interfaces, or subinterfaces, on a single physical interface allows greater flexibility and connectivity on the network.

Protocols such as Frame Relay and ATM require that you create one or more virtual circuits over which your data traffic is transmitted to higher layers in the protocol stack. The system requires that you define a subinterface on top of a physical interface as a platform for a virtual circuit, such as a permanent virtual circuit (PVC).

Once you have defined the underlying characteristics of an interface, use the interface command to:

1. Assign an interface type, such as POS or ATM.
2. Assign the associated interface specifier to the interface, such as the slot/port and channel/subchannel.
3. Assign one or more subinterfaces.

interface Command

The interface command has the following format:

interface interfaceType interfaceSpecifier

Each interface type has an interface specifier associated with it. The interface specifier identifies the physical location of the interface on the system, such as the chassis slot and port number, and logical interface information, such as an T1 channel on an Channelized T3 interface.

The system supports the interface types shown in Table 1-2.

Table 1-2 Interface types 

Interface Type Variable	Interface Specifier Variable	To configure, see ...
atm	slot/port[.subinterface]	ERX Link Layer Configuration Guide, Chapter 1, Configuring ATM
ethernet	slot/port.subinterface	ERX Physical Layer Configuration Guide, Chapter 6, Configuring Ethernet Interfaces
hssi	slot/port	ERX Physical Layer Configuration Guide, Chapter 7, Configuring HSSIs
loopback	loopback number	ERX Command Reference Guide
mlframe-relay	bundle-name [.subinterface ]	ERX Link Layer Configuration Guide, Chapter 2, Configuring Frame Relay
mlppp	bundle-name	ERX Link Layer Configuration Guide, Chapter 6, Configuring Multilink PPP
pos	slot/port	ERX Link Layer Configuration Guide, Chapter 5, Configuring Packet over SONET
serial	Depends on type of interface	ERX Physical Layer Configuration Guide, Chapter 1, Configuring Channelized T3 Interfaces ERX Physical Layer Configuration Guide, Chapter 2, Configuring T3 and E3 Interfaces ERX Physical Layer Configuration Guide, Chapter 1, Configuring Channelized T3 Interfaces ERX Physical Layer Configuration Guide, Chapter 5, Configuring Channelized OCx/STMx Interfaces ERX Physical Layer Configuration Guide, Chapter 8, Configuring X.21/V.35 Interfaces
tunnel	tunnel-type:tunnel-name	ERX Routing Protocols Configuration Guide, Vol. 1, Chapter 5, Configuring IP Tunnels ERX Routing Protocols Configuration Guide, Vol. 1, Chapter 11, Configuring IPSec ERX Broadband Access Configuration Guide, Chapter 5, Configuring L2TP
null	0	ERX Command Reference Guide and ERX Routing Protocols Configuration Guide, Vol. 1, Chapter 1, Configuring Routing Policy.

For detailed information about interface types and specifiers and for specific syntax for the interface command, see the ERX Command Reference Guide.