有关DSCP的介绍

　　DSCP Values

　　Up to eight DSCP values can be matched in one match statement. For example, if you wanted the DCSP values of 0, 1, 2, 3, 4, 5, 6, or 7 (note that only one of the IP DSCP values must be a successful match criterion, not all of the specified DSCP values), enter the match dscp 0 1 2 3 4 5 6 7 command.

　　This command is used by the class map to identify a specific DSCP value marking on a packet. In this context, dscp-value arguments are used as markings only and have no mathematical significance. For instance, the dscp-value of 2 is not greater than 1. The value simply indicates that a packet marked with the dscp-value of 2 is different from a packet marked with the dscp-value of 1. The treatment of these marked packets is defined by the user through the setting of QoS policies in policy-map class configuration mode.

　　Match IPv6 Packets on DSCP Values

　　To match DSCP values for IPv6 packets only, the match protocol ipv6 command must also be used. Without that command, the DSCP match defaults to match both IPv4 and IPv6 packets.

　　Match IPv4 Packets on DSCP Values

　　To match DSCP values for IPv4 packets only, use the ip keyword. Without the ip keyword, the match occurs on both IPv4 and IPv6 packets. Alternatively, the match protocol ip command can be used with the match dscp command to classify only IPv4 packets.

　　Examples

　　Priority50 Service Policy Matching DSCP Value

　　The following example shows how to configure the service policy called "priority50" and attach service policy "priority50" to an interface. In this example, the class map called "ipdscp15" will evaluate all packets entering interface Fast Ethernet 1/0/0 for an IP DSCP value of 15. If the incoming packet has been marked with the IP DSCP value of 15, the packet will be treated as priority traffic and will be allocated with bandwidth of 50 kbps.

　　Router(config)# class-map ipdscp15

　　Router(config-cmap)# match ip dscp 15

　　Router(config)# exit

　　Router(config)# policy-map priority50

　　Router(config-pmap)# class ipdscp15

　　Router(config-pmap-c)# priority 50

　　Router(config-pmap-c)# exit

　　Router(config-pmap)# exit

　　Router(config)# interface fa1/0/0

　　Router(config-if)# service-policy output priority50