You want the router to mark the DSCP or TOS field of an IP packet to affect its priority through the network.
The solution to this problem depends on the sort of traffic distinctions you want to make, as well the version of IOS you are running in your routers.
There must be something that defines the different types of
traffic that you wish to prioritize. In general, the simpler the
distinctions are to make, the better. This is because all of the tests
take router resources and introduce processing delays. The most common
rules for distinguishing between traffic types use the packet’s input interface and
simple IP header information such as TCP port numbers. The following
examples show how to set an IP Precedence value of immediate (2) for all FTP control
traffic that arrives through the
serial0/0 interface, and an IP Precedence of
priority (1) for all FTP data traffic. This distinction is possible
because FTP control traffic uses TCP port 21, and FTP data uses port
The new method for configuring this uses class maps. Cisco first introduced this feature in IOS Version 12.0(5)T. This method first defines a class-map that specifies how the router will identify this type of traffic. It then defines a policy-map that actually makes the changes to the packet’s TOS field:
configure terminalEnter configuration commands, one per line. End with CNTL/Z. Router(config)#
permit any eq