Cisco Catalyst 2000 Configuration Handbook page 251

230 Cisco LAN Switching Configuration Handbook
d. (Optional) Trust the inbound IP precedence value by default.
Note that no drop precedences are used by default. This gives DSCP values
that differ slightly from those shown in Table 13-2 because the drop prece-
dence bits are all 000. When you need to map CoS to DSCP values in a
switch, alter the default mapping so that distinct drop precedences are used
instead. To return to the default mapping, use the clear qos cos-dscp-map
or no mls qos map cos-dscp command.
■ Enable CoS trust on one or more ports:
(interface) mls qos trust cos
Trust only the inbound CoS value, from which the ToS or DSCP values will
be derived.
■ Map IP precedence to internal DSCP values:
(global) mls qos map ip-prec-dscp dscp1 ... dscp8
The IP precedence values (0 through 7, or routine, priority, immediate,
flash, flash-override, critical, internet, and network) from inbound packets
are mapped to the corresponding 8 dscp1 through dscp8 values (0 to 63;
defaults are 0, 8, 16, 24, 32, 40, 48, and 56). The resulting internal DSCP val-
ues are then used by QoS. The following table shows the default mapping.
ToS
0 (routine)
1 (priority)
2 (immediate)
3 (flash)
4 (flash-override)
5 (critical)
6 (internet)
7 (network)
Note that no drop precedences are used by default. This gives DSCP values
that differ slightly from those shown in Table 13-2 because the drop prece-
dence bits are all 000. When you need to map CoS to DSCP values in a
switch, alter the default mapping so that distinct drop precedences are used
instead. To return to the default mapping, use the clear qos ipprec-dscp-
map or no mls qos map ip-prec-dscp command.
■ Enable IP precedence trust on one or more ports:
(interface) mls qos trust ip-precedence
Trust only the inbound IP precedence value (ToS), from which the DSCP val-
ues will be derived.
DSCP
0 ("best effort")
8 (AF class 1 "best effort")
16 (AF class 2 "best effort")
24 (AF class 3 "best effort")
32 (AF class 4 "best effort")
40 (EF "best effort")
48 (Internetwork control "best effort")
56 (Network control "best effort")