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98Chapter 12 - Filters and Rules
Cyclades-PR1000
An example showing the third type of traffic control is given in Figure 12.8. The network administrator wants to prioritize
the access to his web server. He also wants to prioritize e-mail sent by his SMTP server, but the priority should be
lower. All other traffic should have the lowest priority. For web server access, the important flow direction is not the
user requests, but rather the data requested. The traffic control rule must be placed on link 2. In the case of e-mail,
the important flow is the data leaving the e-mail server, and not the acknowledgements back. This is also governed by
link 2. (Note: flow control could be placed on the data request packets and the SMTP acknowledgements by associating
rules to link 1.)
Web Server
E-mail Server
Web Client
E-mail Server
PR1000
Requests
ACKs Back
Data Requested
E-mail out
Port: 80
Port: 25 (SMTP)
Port: Any
Link 2
Link 1
Port: Any
INTERNET
FIGURE 12.8 TRAFFIC RULE EXAMPLE 2