Policy Routing for Fun and Profit
The policy routing works perfectly as programmed, directing the traffic as appropriate to the T1 and ADSL links and providing redundancy in case the ADSL link fails. The traffic management on the T1 has been satisfactory, and we generally have been able to provide our users with a respectable service transparently. Of course, the consistency of traffic throughput during a single month is dependent on how rapidly the free bandwidth is consumed.
As an example of our T1 traffic management see Figure 5, which shows Frame Relay T1 bandwidth usage during May 2003. The red line on the graph represents 128kbps, which is our threshold limit for billing. Throughput clamping occurred after May 23. One of our customer's servers became infected with a virus that generated a great deal of traffic during the month, consuming our precious free bandwidth. As a result, these customers were required to exist for more than a week running at 128kbps on the T1 line. ADSL traffic, of course, was not affected.
The same data presented with the five-minute bins listed by bandwidth is shown in Figure 6. This graph may be compared with the ideal usage shown in Figure 3. Notice the billing rate of 122.07kbps indicated in this figure. This reflects the success of the traffic control procedures in ensuring that the billing rate remained below 128kbps.
Although this is quite a simple implementation of policy routing, IP accounting and traffic shaping, it does provide an illustration of how the Linux advanced routing tools can provide the kind of control needed to manage sophisticated traffic policies.
David Mandelstam is President of Sangoma Technologies Corp. Founded in 1984, Sangoma develops and manufactures wide area network (WAN) communication hardware and software products, with an emphasis on the PC platform. The communications solutions and routing products support all popular WAN networks, line protocols and all standard PC operating systems and platforms.
Nenad Corbic is Senior Linux Developer at Sangoma Technologies Corp. (www.sangoma.com).
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