Enterasys Networks X-PeditionTM manual Describing Traffic Policing, Configuring Traffic Policing

Mechanisms Providing QoS

excess bandwidth may be used by CBWFQ. A rule of thumb for configuring PQs is to assign time- sensitive traffic (voice and video) to PQs and other types (e.g., Telnet) to fair queues. Any traffic you do not specially assign (e.g., Email) is automatically directed to the class-defaultqueue. All (100%) of your traffic should not be assigned to PQs - a smaller percentage of lower priority traffic should be designated for fair queues of left unassigned for the default queue.

Internally, the priority queue uses a Token Bucket that measures the offered load and ensures that the traffic stream conforms to the configured rate. Only traffic that conforms to the token bucket is guaranteed low latency. Any excess traffic is dropped even when the link is not congested.

The priority command also sets burst size, a network value used to accommodate temporary bursts of traffic. The default burst value, which is computed as 1 second of traffic at the configured bandwidth rate, is used when the burst argument is not specified.

The XSR allows the priority queue size to grow as much as allowed by the traffic meter.

The following example illustrates priority configuration options and how they are invoked on a Frame Relay port. Begin by creating traffic class frost:

XSR(config)#class-map frost

XSR(config-cmap<frost>)#match access-group 10

Assign the class frost to the priority queue:

XSR(config)#policy-map frame1

XSR(config-pmap<frame1>)#class frost

XSR(config-pmap-c<frost>)#priority high 20

XSR(config-pmap-c<frost>)#queue-limit 30

Describing Traffic Policing

The XSR’s traffic policer lets you examine traffic flows and either discard or mark packets that exceed Service Level Agreement (SLA) Agents. Policing is most frequently used on the network border to ensure that a peer is not consuming more than its allocated bandwidth. A policer will accept traffic up to a certain rate then perform an action on traffic exceeding this rate (out-of- bound traffic). If the policer determines that the packet is out of profile, the packet is either dropped immediately or admitted to the network but marked as out of profile.

The XSR’s implementation of traffic policing provides these benefits:

•Per traffic class bandwidth management permitting control of the maximum rate of traffic sent or received per traffic class.

•Configuration of the policer using maximum rate, normal burst and excess burst. Based on configured values, the policer separates packets into three conformance levels: packets received below the maximum rate are conforming, packets received as excess packets are exceed packets and out-of-bounds packets are violate.

•Marking of packets based conformance levels. You may specify a different action for each conforming level: drop, transmit and/or mark the packet. Also, you may choose to mark the DSCP, IP precedence or CoS field of the packet.

Configuring Traffic Policing

Configuring traffic policing requires creating a traffic class and attaching the policy to an interface or DLCI. The police command specifies the following options:

•Bandwidth, burst and excess burst values

•Action to take for traffic that conforms or exceeds the specified rate

12-6 Configuring Quality of Service