Cabletron Systems SSIM-R8-02 Spécifications télécharger pdf (Page 341)

Enterasys Xpedition User Reference Manual 321

ToS Rewrite

The ToS byte rewrite is part of the QoS priority classifier group. The entire ToS byte can be

rewritten or only the precedence part of the ToS byte can be rewritten. If you specify a

value for <tos-precedence-rewrite>, then only the upper three bits of the ToS byte are

changed. If you set <tos-precedence-rewrite> to any and specify a value for <tos-rewrite>,

then the upper three bits remain unchanged and the lower five bits are rewritten. If you

specify values for both <tos-precedence-rewrite> and <tos-rewrite>, then the upper three bits

are rewritten to the <tos-precedence-rewrite> value and the lower five bits are rewritten to

the <tos-rewrite> value.

For example, the following command will rewrite the ToS Precedence field to 7 if the ToS

Precedence field of the incoming packet is 6:

In the above example, the <tos> value of 222 (binary value 1101 1110) and the <tos-mask>

value of 224 (binary value 1110 0000) are ANDed together to specify the ToS Precedence

field value of 6 (binary value 110). Changing the value in the <tos-mask> parameter

determines the bit in the ToS octet field that will be examined.

The following example will rewrite the ToS Precedence and the ToS fields to 5 and 30 if the

incoming packet is from the 10.10.10.0/24 network with the ToS Precedence field set to 2

and the ToS field set to 7. (In this example, the MBZ bit is included in the ToS field.) The

figure below shows how the parameter values are derived.

The <tos-mask> value determines the ToS bit to be examined, which is all eight bits in this

example. The following command configures the ToS rewrite for the example:

ssr(config)# qos set ip tosp6to7 low any any any any 222 any any 224 7

0000

111

11111

11 1

11111

Incoming Packet:

<tos> = 71

ToS Precedence = 2 ToS = 7

Mask (look at

<tos-mask> = 255

ToS Precedence = 5 ToS = 30

<tos-precedence-rewrite> = 5

<tos-rewrite> = 30

Rewritten ToS byte

for 10.10.10.0/24

packet:

all bits):

ssr(config)# qos set ip tos30to7 low 10.10.10.0/24 any any any 71 any any 255 5 30

1 2 ... 336 337 338 339 340 341 342 343 344 345 346 ... 393 394

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Cabletron Systems SSIM-R8-02 Spécifications Page 341