- Enterasys Security Router User's Guide

Mechanisms Providing QoS
XSR User’s Guide 12-3
features in the traffic policy determine how to treat the classified traffic. Traffic policy cannot be
applied to multilink PPP interfaces at this time.
You must perform three steps to configure a class-based classifier:
1. Define a traffic class with the
class-map command.
2. Create a traffic policy by associating the traffic class with one or more QoS features (using the
policy-map command).
3. Attach the traffic policy to the port or DLCI with the
service-policy command.
A QoS policy-map for DLCI defines a set of complex rules to identify classes of traffic and then
applies service policies to them. Use the traffic-class-map to group a set of simple rules to form a
set of complex rules. You can define complex rules with a combination of matching criteria and, at
the same time, not matching other criteria.
Describing the Class Map
The traffic class map builds complex rules with matching criteria. Multiple rules can be specified
by a given traffic class-map using the
class-map command, but all rules in the given class map
must be configured to use the same matching criteria:
–match-any
–match-all
The following traffic class map defines the match-all class-map abc. A packet that satisfies the
criteria defined in access-group 2 and has a DSCP value set to 32 is considered a part of this traffic
class. In a match-all class-map all criteria must be met in order for the packet to be assigned to the
class.
XSR(config)#access-list 2 permit 15.15.15.0 0.0.0.255
XSR(config)#class-map match-all abc
XSR(config-cmap<abc>)#match access-group 2
XSR(config-cmap<abc>)#match ip dscp 32
In a match-any class-map, one or more criteria of the class-map must be met in order for packets to
be assigned to the class. For example, if class-map ABC were a match-any class-map, packets
arriving with a source address of 15.15.15.3, with Layer 3 protocol IP and DSCP value of 12
assigned, would be classified as class ABC since it matches access-list 2.
Describing the Policy Map
The policy statement in a QoS policy-map specifies how traffic defined by the traffic class-map
will be treated. Each class in policy-map has to be assigned to one of the two types of queues:
CBWFQ or Priority Queue. This includes specifying the following:
•The bandwidth command assigns traffic from this class to a Class- Based Weight Fair Queue
(CBWFQ) with the specified bandwidth. A CBWFQ shares the output link with other
CBWFQs on the same link in proportion to its specified bandwidth or weight. During
congestion, queues are serviced (assigned bandwidth) in proportion to their weight. When
uncongested, a queue can borrow bandwidth from other queues.
Note: A Dialer interface is similar to a virtual interface in that only after it dials on a resource from a
dialer pool is it able to receive and send data. A policy map applied to a dialer interface is
automatically pushed to the resource (Serial or ISDN interface) that the dialer called on. When the
connection is cleared, the policy map is automatically removed from the resource.