How do I classify Diffserv packets?
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How do I classify Diffserv packets?


Article ID: 165990


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The Type of Service (TOS) field in the IP header is known as the Differentiated Services field, as defined in the Differentiated Services specification (RFC 2474). This 8-bit binary field is divided into the following subfields:

  • IP Precedence subfield, also known as the Class of Service (COS) sub-field, which is a 3-bit field
  • Type of Service (TOS) subfield, which is a 4-bit field
  • Unused bit that is set to zero

Network infrastructure devices set TOS to communicate the quality of service needs for a given data stream, commonly for realtime protocols such as VOIP and streaming media.


You can tell PacketShaper to match on these IP precedence bits during classification of IP protocols, then apply specific policies to manage these traffic types. For example, you could apply a policy that substitutes a different precedence value so that you can control the packet's priority when it reaches the router. For details on using a policy to substitute an IP precedence value, see  Substitute DiffServ Values in PacketGuide.

In the IP Precedence (COS) field, specify the IP precedence value to match. Enter a precedence value from 0 to 7 (where 7 is the highest precedence), or a range of values.

PacketShaper can check the Type of Service (TOS) field in the IP header to match on a service level for an application. Select one of the following values to match:

8 = minimize delay
4 = maximize throughput
2 = maximize reliability
1 = minimize monetary cost
0 = normal service

You might match on this TOS field, then use a policy to change the value. For policy details, see Substitute DiffServ Values in PacketGuide.