
144 Chapter 6: Per-Hop Behavior: Congestion Avoidance and Packet Drop Policy
Frequently Asked Questions
Q — What are some rule-of-thumb values for configuring RED parameters?
A — You can calculate the exponential weighting factor based on the following
formula
5
:
Exponential weighting factor = 10 ÷ B
where B is the output link bandwidth in MTU-size packets.
Because it doesn’t change the end result, use an MTU of 1500 bytes for all links,
even on links with an actual MTU size of 4470 bytes.
For a DS3 (45 Mbps) link,
B = (45 Mbps ÷ 8) ÷ 1500 = 3750.
Therefore, the exponential weighting factor
= 10 ÷ B = 2.67 E – 3
which is approximately equal to 2
-9
.
The exponential ...