Traffic Shaping
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• The ingress interface can have a defined shaper
• When the packet passes through session tracking, the two sides of the session tracking (forward and reverse)
can each have shapers that apply.
• It is possible to create a bonded gateway route where multiple routes exist for the same target (typically a
default gateway) and each route as a speed set, which is itself a shaper. This is used to control how much
traffic goes via each of the bonded routes. (You simply create more than one
route
object with a
speed
or
graph
setting).
• The egress interface can have a defined shaper
10.3. Basic principles
Each shaper tracks how far ahead the link has got with traffic that has been recently sent. This depends on
the length of packets sent and the speed of the shaper. This is, essentially, tracking how much is likely to be
queued at a bottleneck further on. The FB6000 does not delay sending packets and assumes something with a
lower speed is probably queuing them up later.
This record of how far ahead the traffic is gets used in two ways:
• If the shaper is too far ahead, then packets are dropped, causing the link to be rate limited to the selected
speed. Exactly how much is too far depends on the packet size, with small packets (less than 1000 bytes)
allowed more margin than large packets. This has the effect of prioritising DNS, interactive traffic, VoIP, etc.
• Where there are two or more links with shapers a link is picked based on which is the least far ahead. This
has the effect of balancing the traffic levels between multiple links based on the speed of each link exactly.
