Hierarchical Rate Limits ! 79
Chapter 3: Creating Rate-Limit Profiles
Rate-Limit Profiles
Hierarchical rate-limit profiles are independent from interface types. You can apply
the green, yellow, or red mark values to the rate-limit profile for every type of
forwarding interface that accepts ToS marking for packets. The same rate limit can
be reused for a different interface type. Hierarchical rate limits have two-rate or
TCP-friendly rate types.
The value applied to the ToS field is configured in the CLACL group for green, yellow,
or red packets but the coloring of the packet as green, yellow, or red depends on the
entire rate-limit hierarchy.
! Preferred packets are transmitted unconditionally. Rate limits that process
packets transmitted unconditionally always decrement their token count, if
necessary, making it negative.
! Red packets cannot be transmitted unconditionally, to avoid cases where an
aggregate rate limit is oversubscribed with transmit-unconditional rates.
! Color-aware uses the incoming packet color in its algorithm
! Not promoting packets means that if the packet enters the rate limit as yellow
and the rate-limit then determines that it is green, the packet remains yellow. If
the rate limit determines it is red, then the packet is colored red.
A rate-limit rule is an instance of a rate-limit profile. The same profile can be used to
create many rate-limit rules in the same hierarchy or in different rate-limit
hierarchies. The classifier group that defines the flow can use a mark rule with
color-mark profile to set the packet ToS field based on the packet color. A rate-limit
hierarchy invoked from the classifier group is one way of changing the packet color;
the rate-limit hierarchy is invoked before the classifier group runs the mark rule to
set the packet ToS.
Rate-Limit Actions
Every packet traversing a rate-limit hierarchy has an owner that is defined by the
last rate limit that can apply its actions to the packet; this is a configuration option.
A rate limit in the hierarchy that does not own the packet only decrements its
tokens, but cannot perform any of the following actions:
! Transfer ownership of the packet to the next rate limit.
! Retain ownership of the packet but consume tokens from the remaining rate
limits in the hierarchy.
! Exit the rate-limit hierarchy, making that rate limit the final one for the packet.
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