s will require some investigative work on your part. You should interview all the business groups that use the network, and deter- mine what protocols are important to them. Assume from the onset that every one them will tell you that their protocols are the most important, and should get the lion's share of the bandwidth. You will need to assimilate all of this data, and make some decisions about how to allocate the bandwidth. With the help of good management, you should be able to come up with a list of requirements from which you can work. Protocols Compile a list of the protocols in use on your network. Tools to help you with this task include packet-capture applications such as Ethereal, netflow switching on Cisco routers, and Network Analysis Modules in 6500 switches. Take careful notes. Also, bear in mind that companies like to change the default ports for popular protocols. You might have web traffic on ports 80, 443, and 8080, for example. Record who is using each protocol, and how the protocols behave. Some protocols can be tricky. For example, RTP is used for the voice stream of Cisco VoIP. If you assume that all RTP packets should get top priority to ensure voice quality, there may be unintended consequences. Other applications, such as streaming video, may also use RTP. If you design a QoS scheme that prioritizes RTP at the highest level without any further granularity, video conferencing could cause quality problems in voice calls. If you know that video conferencing is only done from the executive boardroom, however, you can prioritize that traffic accordingly to avoid problems. Priorities Determining priorities can be tough. Politics may well play a part in this step, SO be prepared to play the game. There are certain best practices for QoS. For example: You shouldn't use IP precedence 6 and 7, as they are reserved for internetwork control and network control. Voice RTP packets should always be marked IP precedence 5 (DSCP: EF). All voice-control packets should be marked IP precedence 3 (DSCP: AF3