Loopback Interfaces - IBM RackSwitch G8000 Application Manual

Loopback Interfaces

© Copyright IBM Corp. 2011
A loopback interface provides an IP address, but is not otherwise associated with a
physical port or network entity. Essentially, it is a virtual interface that is perceived as
being "always available" for higher-layer protocols to use and advertise to the
network, regardless of other connectivity.
Loopback interfaces improve switch access, increase reliability, security, and
provide greater flexibility in Layer 3 network designs. They can be used for many
different purposes, but are most commonly for management IP addresses, router
IDs for various protocols, and persistent peer IDs for neighbor relationships.
In IBM N/OS 6.8, loopback interfaces have been expanded for use with routing
protocols such as OSPF and BGP. Loopback interfaces can also be specified as the
source IP address for syslog, SNMP, RADIUS, TACACS+, NTP, and router IDs.
Loopback interfaces must be configured before they can be used in other features.
Up to five loopback interfaces are currently supported. They can be configured
using the following commands:
RS G8000(config)# interface loopback <1-5>
RS G8000(config-ip-loopback)# [no] ip address <IPv4 address> <mask> enable
RS G8000(config-ip-loopback)# exit
Using Loopback Interfaces for Source IP Addresses
The switch can use loopback interfaces to set the source IP addresses for a variety
of protocols. This assists in server security, as the server for each protocol can be
configured to accept protocol packets only from the expected loopback address
block. It may also make is easier to locate or process protocol information, since
packets have the source IP address of the loopback interface, rather than numerous
egress interfaces.
Configured loopback interfaces can be applied to the following protocols:
• Syslogs
RS G8000(config)# logging source-interface loopback <1-5>
• SNMP traps
RS G8000(config)# snmp-server trap-source loopback <1-5>
• RADIUS
RS G8000(config)# ip radius source-interface loopback <1-5>
• TACACS+
RS G8000(config)# ip tacacs source-interface loopback <1-5>
• NTP
RS G8000(config)# ntp source loopback <1-5>
Loopback Interface Limitation
• ARP is not supported. Loopback interfaces will ignore ARP requests.
• Loopback interfaces cannot be assigned to a VLAN.
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Chapter 2. Initial Setup