What Are Loopback Interfaces - Dell Networking 7048 Configuration Manual

For each VLAN routing interface you can assign a static IP address, or you can
allow a network DHCP server to assign a dynamic IP address.
When a port is enabled for bridging (L2 switching) rather than routing,
which is the default, all normal bridge processing is performed for an inbound
packet, which is then associated with a VLAN. Its MAC Destination Address
(MAC DA) and VLAN ID are used to search the MAC address table. If
routing is enabled for the VLAN, and the MAC DA of an inbound unicast
packet is that of the internal router interface, the packet is routed. An
inbound multicast packet is forwarded to all ports in the VLAN, plus the
internal bridge-router interface, if it was received on a routed VLAN.
Since a port can be configured to belong to more than one VLAN, VLAN
routing might be enabled for all of the VLANs on the port or for only some of
the VLANs on the port. VLAN Routing can be used to allow more than one
physical port to reside on the same subnet. It could also be used when a
VLAN spans multiple physical networks, or when additional segmentation or
security is required.

What Are Loopback Interfaces?

A loopback interface is a logical interface that is always up and, because it
cannot go down, allows the switch to have a stable IP address that other
network devices and protocols can use to reach the switch. The loopback can
provide the source address for sent packets.
NOTE:
In this context, loopback interfaces should not be confused with the
loopback IP address, usually 127.0.0.1, assigned to a host for handling self-routed
packets.
The loopback interface does not behave like a network switching port.
Specifically, there are no neighbors on a loopback interface; it is a pseudo-
device for assigning local addresses so that the other layer 3 devices can
communicate with the switch by using the loopback IP address. The loopback
interface is always up and can receive traffic from any of the existing active
interfaces. Thus, given reachability from a remote client, the address of the
loopback can be used to communicate with the switch through various
services such as Telnet and SSH. In this way, the IP address on a loopback
behaves identically to any of the local addresses of the VLAN routing
interfaces in terms of the processing of incoming packets.
844
Configuring Routing Interfaces