Logical Interface Configuration; Logical Interface Overview; Dialer Interface; Loopback Interface - 3Com MSR 50 Series Configuration Manual

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Logical Interface
Overview

Dialer Interface

Loopback Interface

Introduction to
Loopback Interface
L
OGICAL
n
This section introduces basic configurations about logical interfaces. For the
configurations about the data link layer, network layer and some special features,
refer to the relevant sections in the Access Volume and IP Service Volume.
A logical interface (also known as virtual interface) refers to an interface that can
implements data switching but does not exist physically. Logical interfaces include
dial interfaces, loopback interfaces, null interfaces, sub-interfaces, multilink
point-to-point protocol group (MP-group) interfaces, multilink frame relay (MFR)
interfaces, backup center logical channels, virtual templates (VTs), and so on.
A dialer interface is designed for configuring dial control center (DCC) parameters.
A physical interface can inherit configuration information through binding itself to
a dialer interface. The following interfaces on a device support dialing:
asynchronous serial interfaces (including synchronous/asynchronous serial
interfaces operating in asynchronous mode), AUX interfaces, AM interfaces, ISDN
BRI interfaces and ISDN PRI interfaces.
DCC is a routing technology used for interconnecting routers through public
switched network (PSTN or ISDN), and DCC provides dial-on-demand service. In
some occasions, channels are established and communication is implemented
among routers only when necessary, so the information transmitted between
routers is bursty and small-sized. DCC provides a flexible and economic solution
for such implementations.
n
Refer to "DCC Configuration" on page 153
A loopback interface is a software-only virtual interface. The physical layer state
and link layer protocols of a loopback interface are always up except when the
loopback interface is manually shut down. A loopback interface can be configured
with an IP address. For saving IP address resources, the IP address of an loopback
interface is coupled with a 32-bit mask. Routing protocols can be enabled on a
loopback interface, and a loopback interface is capable of sending and receiving
routing protocol packets.
Loopback interfaces have various uses, for example, the IP address of a loopback
interface can be used as the source addresses of all the IP packets that the local
device generates. As loopback interface addresses are stable and are unicast
addresses, they are usually used to identify devices. In some cases, configuring an
I
NTERFACE
C
ONFIGURATION
for more information about DCC.