Cisco 300 Series

Introduction
39 OL-32830-01 Command Line Interface Reference Guide
1
A loopback interface does not support bridging; it cannot be a member of any
VLAN, and no layer 2 protocol can be enabled on it.
Layer 3 Specification
IP Interface
IPv4 and IPv6 addresses can be assigned to a loopback interface.
The IPv6 link-local interface identifier is 1.
Routing Protocols
A routing protocol running on the switch supports the advertising of the IP prefixes
defined on the loopback interfaces via the routing protocol redistribution
mechanism.
If a layer 2 switch with one IPv4 address supports a loopback interface, the above
rules are replaced by the following ones:
This is the definition of the IP configuration when the device is in layer 2 mode:
• Only one loopback interface is supported.
• Two IPv4 interfaces can be configured: one on a VLAN and one on the
loopback interface.
• If the IPv4 address was configured on the default VLAN and the default
VLAN is changed, the switch moves the IPv4 address to the new default
VLAN.
• The ip address command does the following:
- In VLAN context, it replaces the existing configured IPv4 address on the
specified interface by the new one.
- In VLAN context, it supports the keyword default-gateway.
- In Loopback Interface context, it replaces the existing, configured IPv4
address on the loopback interface with the new one.
- In the Loopback Interface context, it does not support the keyword
default-gateway.