Switch Operation Overview; Address Table Operation - HP ProCurve 224 Installation Manual

Switch Operation Overview

Address Table Operation

Address Learning. As devices are connected to the switch ports, either
directly or through hubs or other switches that are connected to the switch,
the MAC addresses of those devices are learned automatically and stored in
the Switch 212M/224M's 2048-entry address table. The switch also identifies
the number of the port on which each address is learned so it knows the
network location of each device.
Forwarding, Filtering, Flooding. When the switch receives a packet, it
determines the destination address and looks for the address in the address
table. Based on the port location of that address, the switch then determines
whether to forward, filter-out, or flood the packet.
forward - if the destination address is on a different port than the one on
which the packet was received, the packet is forwarded to the destination
port and on to the destination device.
filter out - if the destination address is on the same port as the one on
which the packet was received, the packet is filtered out. The switch
thereby isolates local traffic so the rest of the network connected to the
switch does not lose bandwidth dealing with unnecessary traffic.
flood - whenever a new destination address is found in a packet received
on one of the switch ports, the destination address will not yet be in the
switch's address table and the Switch 212M/224M cannot know whether
to forward or filter out the packet. In this case, it sends the packet to all
the other ports. This is referred to as "flooding". When the destination
device receives the packet, it replies, and the switch learns the new
address from the reply packet. Then, all future packets destined for that
address are forwarded or filtered out appropriately.
Network Moves and Changes. When devices are moved in the network,
and become connected to a different switch port, the Switch 212M/224M
automatically recognizes the change and updates the address table with the
new port location of the device. Communication with the device is automati-
cally maintained, without any address table manipulation being required.
Introducing the HP ProCurve Switch 212M and 224M
Switch Operation Overview
1-7