Cabletron Systems SMARTSWITCH ROUTER 9032578-05 - Manual (Page 318)

Chapter 21: QoS Configuration Guide
292 SmartSwitch Router User Reference Manual
Within the SSR, QoS policies are used to classify Layer-2, Layer-3, and Layer-4 traffic into
the following priority queues (in order from highest priority to lowest):
• Control (for router control traffic; the remaining classes are for normal data flows)
• High
• Medium
• Low
Separate buffer space is allocated to each of these four priority queues. By default,
buffered traffic in higher priority queues is forwarded ahead of pending traffic in lower
priority queues (this is the strict priority queuing policy). During heavy loads, low-priority
traffic can be dropped to preserve the throughput of the higher-priority traffic. This
ensures that critical traffic will reach its destination even if the exit ports for the traffic are
experiencing greater-than-maximum utilization. To prevent low-priority traffic from
waiting indefinitely as higher-priority traffic is sent, you can apply the weighted fair
queuing (WFQ) queuing policy to set a minimum bandwidth for each class. You can also
apply weighted random early detection (WRED) to keep congestion of TCP traffic under
control.
Layer-2 and Layer-3 & Layer-4 Flow Specification
In the SSR, traffic classification is accomplished by mapping Layer-2, -3, or -4 traffic to one
of the four priorities. Each traffic classification is treated as an individual traffic flow in the
SSR.
For Layer-2 traffic, you can define a flow based on the following:
• MAC packet header fields, including source MAC address, destination MAC address
and VLAN IDs. A list of incoming ports can also be specified.
For Layer-3 (IP and IPX) traffic, you can define “flows”, blueprints or templates of IP and
IPX packet headers.
• The IP fields are source IP address, destination IP address, UDP/TCP source port,
UDP/TCP destination port, TOS (Type of Service), transport protocol (TCP or UDP),
and a list of incoming interfaces.
• The IPX fields are source network, source node, destination network, destination node,
source port, destination port, and a list of incoming interfaces.
For Layer-4 traffic, you can define a flow based on source/destination TCP/UDP port
number in addition to Layer-3 source/destination IP address.
The flows specify the contents of these fields. If you do not enter a value for a field, a
wildcard value (all values acceptable) is assumed for the field.