Nortel Networks 8000 - Manual (Page 105)

5 Logical interface configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
OQ NOTE
The SR8000 is an integrated device. The numbering of the Virtual-Ethemet interface must follow certain
limitations. The slot number and card number are fixed as 0.
5.1.4 Loopback interface
Loopback is a virtual interface with the characteristic of software.
TCP/IP specifies that the IP addresses in the network segment 127.0.0.0 are loopback
addresses. Interfaces that are of loopback addresses are loopback interfaces.
On startup, the system creates a loopback interface with address 127.0.0.1 to receive packets
which are sent to this system. This address cannot be configured or advertised with routing
protocols.
Certain applications need to configure a local interface with a specific IP address without
influence on the physical interface configuration. In addition, the IP address should be
configured with a 32-bit mask to save IP addresses, and can be advertised with routing
protocols. Loopback interfaces are used to resolve such applications.
5.1.5 Null interface
The Null interface is also a virtual interface with the characteristic of software. Compared
with a loopback interface, a Null interface is like the null devices supported in some operating
systems. Any packet that is sent to a Null interface is dropped.
5.2 Creating sub-interfaces
5.2.1 Establishing the configuration task
Applicable environment
You use the sub-interfaces to provide multiple links on one physical interface. The following
WAN physical interfaces support sub-interfaces:
• Interfaces of FR encapsulation
• Interfaces of X.25 encapsulation
• ATM interface
Preconfiguration tasks
Before configuring a sub-interface, connect and configure the corresponding physical
interface properly.
Data preparation
To create the sub-interface, you need the following data.
No. Data
Number of the main interface
5-4 Nortel Networks Inc. Issue 5.3 (30 March 2009)
1