Loopback Interface - Cisco 500 Series Administration Manual

18
IP Configuration
Overview
Layer 3 IP Addressing
In Layer 3 system mode, the device can have multiple IP addresses. Each IP
address can be assigned to specified ports, LAGs, or VLANs. These IP addresses
are configured in the IPv4 Interface and IPv6 Interfaces pages in Layer 3 system
mode. This provides more network flexibility than the Layer 2 system mode, in
which only a single IP address can be configured. Operating in Layer 3 system
mode, the device can be reached at all its IP addresses from the corresponding
interfaces.
A predefined, default route is not provided in Layer 3 system mode. To remotely
manage the device, a default route must be defined. All DHCP-assigned default
gateways are stored as default routes. In addition, you can manually define default
routes. This is defined in the IPv4 Static Routes and IPv6 Routes pages.
All the IP addresses configured or assigned to the device are referred to as
Management IP addresses in this guide.
If the pages for Layer 2 and Layer 3 are different, both versions are displayed.

Loopback Interface

Overview
The loopback interface is a virtual interface whose operational state is always up.
If the IP address that is configured on this virtual interface is used as the local
address when communicating with remote IP applications, the communication will
not be aborted even if the actual route to the remote application was changed.
The operational state of a loopback interface is always up. You define an IP
address (either IPv4 or IPv6) on it and use this IP address as the local IP address
for IP communication with remote IP applications. Communication remains intact
as long as the remote applications can be reached from any one of the switch's
active (non-loopback) IP interfaces. On the other hand, if the IP address of an IP
interface is used in communicating with remote applications, the communication
will be terminated when the IP interface is down.
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.
The IPv6 link-local interface identifier is 1.
When the switch is in Layer 2 system mode, the following rules are supported:
• Only one loopback interface is supported.
343 Cisco 500 Series Managed Switch Administration Guide