Allied Telesis AT-S62 - Manual (Page 220)

Chapter 14: Classifiers
Section II: Advanced Operations 220
Classifier Overview
A classifier defines a traffic flow. A traffic flow consists of packets that
share one or more characteristics. A traffic flow can range from being
very broad to very specific. An example of the former might be all IP
traffic while an example of the latter could be packets with specific
source and destination MAC addresses.
A classifier consists of a set of criteria. You configure the criteria to match
the traffic flow you want the classifier to define. Examples of the
variables include source and destination MAC addresses, source and
destination IP addresses, IP protocols, source and destination TCP and
UDP ports numbers, and so on. You can also specify more than one
criteria within a classifier to make the definition of the traffic flow more
specific. Some of the variables you can mix-and-match, but there are
restrictions, as explained later in this section in the descriptions of the
individual variables.
By itself, a classifier does not perform any action or produce any result
because it lacks instructions on what a port should do when it receives a
packet that belongs to the defined traffic flow. Rather, the action is
established outside the classifier. As a result, you will never use a
classifier by itself.
There are two AT-S62 features that use classifiers. They are:
❑ Access control lists (ACL)
❑ Quality of Service (QoS) policies
As explained in Chapter 15 on page 237, an ACL filters ingress packets on
a port by controlling which packets a port will accept and reject. You can
use this feature to improve the security of your network or enhance
network performance by creating network paths dedicated to carrying
specific types of traffic.
When you create an ACL you must specify the traffic flow you want the
ACL to control. You do that by creating one or more classifiers and
adding the classifiers to the ACL. The action that the port takes when an
ingress packet matches the traffic flow specified by a classifier is
contained in the ACL itself. The action will be to either accept packets of
the traffic flow or discard them.
The other feature that uses classifiers is QoS policies. You can use this
feature to regulate the various traffic flows that pass through the switch.
For instance, you might raise or lower the user priority value of a traffic
flow or increase or decrease its allotted bandwidth.