Description

This article describes the defaults of DSCP code points and their standard aliases.

Symptoms

Describing the default code-points in use for DSCP.

Solution

A code-point alias is a name you assign to a set of DiffServ code-point (DSCP) bits. When you configure classes and define classifiers, you can refer to the code points by these alias names. You can configure user-defined classifiers in terms of alias names. If the value of an alias changes, it alters the behavior of any classifier that references that alias.

The table below shows the default mappings between the bit values and standard aliases. For example, it is widely accepted that the alias for DSCP 101110 is ef (expedited forwarding).

Diffserv Designator Mapping
DSCP Code points  
ef 101110
af11 001010
af12 001100
af13 001110
af21 010010
af22 010100
af23 010110
af31 011010
af32 011100
af33 011110
af41 100010
af42 100100
af43 100110
be 000000
cs1 001000
cs2 010000
cs3 011000
cs4 100000
cs5 101000
nc1/cs6 110000
cs2/cs7 111000
MPLS EXP code points  
be 000
be1 001
ef 010
ef1 011
af11 100
af12 101
nc1/cs6 110
nc/cs7 111
IEEE 802.1 code points  
be 000
be1 001
ef 010
ef1 011
af11 100
af12 101
nc1/cs6 110
nc2/cs7 111
Legacy IP Precedence CP  
be 000
be1 001
ef 010
ef1 011
af11 100
af12 101
nc1/cs6 110
nc2/cs7 111

You use code-point aliases to do the following:
  • Define an alias for bits that currently have no alias
  • Define multiple aliases for the same bits
  • Redefine an alias name to mean a different set of bits than the default

To define a code-point alias, include the code-point-aliases statement at the [edit class-of-service] hierarchy level:
[edit class-of-service]
code-point-aliases {
    (dscp | exp | ieee-802.1 | inet-precedence) {
        alias-name bits;
    }
}

For example, you might set up the following configuration:
[edit class-of-service]
code-point-aliases {
    dscp {
        my1 110001;
                   my2 101110;
                   be 000001;
                   cs7 110000;
    }
}

The sample configuration produces this mapping:
user@host>show class-of-service code-point-aliases dscp
Code point type: dscp

Alias            Bit pattern
ef/my2           101110
af11             001010
af12             001100
af13             001110
af21             010010
af22             010100
af23             010110
af31             011010
af32             011100
af33             011110
af41             100010
af42             100100
af43             100110
be               000001
cs1              001000
cs2              010000
cs3              011000
cs4              100000
cs5              101000
nc1/cs6/cs7      110000
nc2              111000
my1              110001

The following notes explain certain results in the mapping:
  • my1 110001:

    • 110001 was not mapped to anything before, and my1 is a new alias.
    • Nothing in the default mapping table is changed by this statement.

  • my2 101110:

    • 101110 is now mapped to my2 as well as ef.

  • be 000001:

    • be is now mapped to 000001.
    • The old value of be, 000000, is not associated with any alias. Packets with this DSCP value are now classified to the default forwarding class.

  • cs7 110000:

    • cs7 is now mapped to 110000, as well as nc1 and cs6.
    • The old value of cs7, 111000, is still mapped to nc2.

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