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136Chapter 14 - Filters and Rules
Cyclades-PR4000
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
PR4000
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