Allied Telesis AT-S62 - Manual (Page 234)

Chapter 13: Classifiers
234 Section II: Advanced Operations
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:
ˆ Access control lists (ACL)
ˆ Quality of Service (QoS) policies
As explained in Chapter 14 on page 251, 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.
As with an ACL, you specify the traffic flow of interest by creating one or
more classifiers and applying them to a QoS policy. The action to be taken
by a port when it receives a packet that corresponds to the prescribed flow