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RFC 2475 defines a field in the layer 3 header of IP packets, called the DiffServ code point (DSCP). Typically, hosts or routers sending traffic into a DiffServ network mark each transmitted packet with the appropriate DSCP. The switch then uses the DSCP to classify packets. You can alternately set the switch to replace the DSCP in a packet with a different DSCP. The switch then uses the new DSCP to classify the packet.
To set the switch to classify IP packets by their DSCP or to replace the DSCP with a different DSCP, you must set up an ACL rule. For information on how to set up an ACL rule to enable DiffServ functionality, see "Setting Up an ACL Rule" later in this chapter.
The Differentiated Services (DiffServ) Mapping Table associates specific DSCP values with specific priorities. You create these associations by assigning priorities to DSCPs. For information on how to assign priorities to DSCPs, see "Assigning a Priority to a DSCP" later in this chapter.
Because the DSCP is located in the layer 3 header, the switch does not typically use the DSCP to classify bridged IP traffic. However, you can set a physical port to use the DSCP to classify bridged IP traffic. For information on how to set a physical port to use DiffServ, see "Setting a Physical Port to Use DiffServ" later in this chapter.
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