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8-15
Configuring IP Addressing
Loopback Interfaces
N o t e
Designating a primary VLAN other than the default VLAN affects the switch’s
use of information received via DHCP/Bootp. For more on this topic, refer to
the chapter describing VLANs in the
Advanced Traffic Management Guide
for your switch.
After you reconfigure or reboot the switch with DHCP/Bootp enabled in a
network providing DHCP/Bootp service, the switch does the following:
■ Receives an IP address and subnet mask and, if configured in the server,
a gateway IP address and the address of a Timep server.
■
If the DHCP/Bootp reply provides information for downloading a config-
uration file, the switch uses TFTP to download the file from the designated
source, then reboots itself. (This assumes that the switch or VLAN has
connectivity to the TFTP file server specified in the reply, that the config-
uration file is correctly named, and that the configuration file exists in the
TFTP directory.)
Loopback Interfaces
This section describes how to configure and use user-defined loopback inter-
faces on the switch.
Introduction
By default, each switch has an internal loopback interface (
lo0
) with the IP
address 127.0.0.1. This IP address is used only for internal traffic transmitted
within the switch and is not used in packet headers in egress traffic sent to
network devices.
You can configure up to seven other loopback interfaces ( lo1 , lo2 , lo3 , and so
on) on the switch to use to transmit network across the network. Each
loopback interface can have multiple IP addresses. Routing protocols, such
as RIP and OSPF, advertise the configured loopback addresses throughout a
network or autonomous system.
User-defined loopback addresses provide the following benefits:
■
A loopback interface is a virtual interface that is always up and reachable
as long as at least one of the IP interfaces on the switch is operational. As
a result, a loopback interface is useful for debugging tasks since its IP
address can always be pinged if any other switch interface is up.
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 15 Monday, January 28, 2008 10:04 AM