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Chapter 15: QoS Configuration Guide
Allocating Bandwidth for a Weighted-Fair Queuing Policy
If you enable the weighted-fair queuing policy on the IA, you can allocate bandwidth for
the queues on the IA. To allocate bandwidth for each IA queue, enter the following
command in Configure mode:
Allocate bandwidth for a
weighted-fair queuing policy.
ToS Rewrite
In the Internet, IP packets that use different paths are subject to delays, as there is little
inherent knowledge of how to optimize the paths for different packets from different
applications or users. The IP protocol actually provides a facility, which has been part of
the IP specification since the protocol's inception, for an application or upper-layer
protocol to specify how a packet should be handled. This facility is called the Type of
Service (ToS) octet.
The ToS octet part of the IP specification, however, has not been widely employed in the
past. The IETF is looking into using the ToS octet to help resolve IP quality problems.
Some newer routing protocols, like OSPF and IS-IS, are designed to be able to examine the
ToS octet and calculate routes based on the type of service.
The ToS octet in the IP datagram header consists of three fields:
7
Precedence
Most Significant Bit
•
The three-bit Precedence field is used to indicate the priority of the datagram.
•
The four-bit ToS field is used to indicate trade-offs between throughput, delay,
reliability, and cost.
•
The one-bit must be zero (MBZ) field is not currently used. (In the IA configuration,
there is no restriction on this bit and it is included as part of the ToS field.)
For example, setting the ToS field to 0010 specifies that a packet will be routed on the most
reliable paths. Setting the ToS field to 1000 specifies that a packet will be routed on the
paths with the least delay. (Refer to RFC 1349 for the specification of the ToS field value.)
238
qos set weighted-fair control
6
5
4
<percentage>
high
medium
<percentage>
low
port
3
2
1
ToS
Least Significant Bit
Internet Appliance User Reference Manual
<percentage>
<percentage>
<port list>
|all-ports
0
MBZ
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