Enterasys Networks X-PeditionTM manual Mechanisms Providing QoS, Traffic Classification

Mechanisms Providing QoS

•QoS on the dialer interfaces is directly applied to the dialer interface and inherited by the dial pool members (Serial or ISDN).

•QoS on MLPPP interfaces.

•QoS on point-to-point and point-to-multi-point VPN interfaces.

•Control over copy of the ToS byte from/to outer header for VPN tunnels.

•QoS on Ethernet port and sub-interfaces (PPPoE and VLAN).

Be aware that QoS service on the XSR is proscribed by the following limits:

•No more than 64 classes permitted

•Traffic policer cannot be set for traffic flows assigned to priority queues. Each priority queue is metered and policed by default to guarantee it conforms to the scheduled traffic pattern

•Priority and bandwidth commands are mutually exclusive; a traffic flow is assigned to either queue, not both

•Tail-drop (queue-limit) and RED (random-detect) are mutually exclusive; a queue is managed by either mechanism, not both

•QoS on Input does not perform the following: packet buffering, shaping, bandwidth sharing, prioritization, CoS bit marking in the VLAN header, RED or WRED

Mechanisms Providing QoS

This section describes the general mechanisms the XSR employs to support Quality of Service.

Traffic Classification

Before the XSR can apply QoS to traffic, it must differentiate between types of traffic. The process is called traffic classification. Table 12-1on page 12-2describes typical traffic classification:

Table 12-1 Traffic Classification

Classification	Description	Additional
Criteria		Comments
IP Precedence bits in	Simple classification for IP packets only. IP Precedence bits reside in the ToS byte	Simple, IP
IP header (IP only)	of the IPv4 header and are 3-bits long, providing up to 8 levels of QoS classes.	traffic only
DSCP (DiffServ	Simple classification for IP packets only. This QoS signaling method is defined by	Simple, IP
Code Point) bits in IP	the IETF DiffServ group providing a scalable QoS solution. It is 6-bits long and can	traffic only
header (IP only)	provide 64 different traffic classes. DSCP overlaps with the IP Precedence bits in
	the IP header and can be considered a super set of IP Precedence.
Multiple-Field	This classification considers the L3 header (source and destination IP addresses),	Most
Classification	L4 header (TCP/UDP port numbers to identify the nature of applications as FTP,	versatile but
	Telnet, Web, etc.), and in some cases, looks at fields beyond the L4 header (e.g., to	CPU
	differentiate Web access to certain Web pages from other Web accesses), to	intensive
	narrow the classification and choose traffic from a particular application.

The XSR provides a class-based traffic classifier that creates traffic policies and attaches them to interfaces, sub-interfaces, and virtual circuits such as Frame Relay DLCIs. A traffic policy contains a traffic class and one or more QoS features. A traffic class is used to classify traffic, while the QoS

12-2 Configuring Quality of Service