From: Lord, Chris (chris.lord@lorien.co.uk)
Date: Fri Dec 17 2004 - 09:03:07 GMT-3
Tim,
It's my understanding that if MISSION-CRITICAL is running flat-out at
32k but the link is not saturated, then the 25% class-default (or what's
left of it) is fair-game for the NON-CRITICAL class. So if you use
"bandwidth" or "shape" you could burst up to 96k theoretically.
Chris.
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: 16 December 2004 18:37
To: Group Study
Subject: Comparing policy-map commands: bandwidth, police, and shape
Hi guys,
This is a summary of what these commands do under different conditions.
I'm
posting this to
help others and to confirm my understanding is 100% correct. If I state
anything that's misleading or incorrect, hopefully,
someone will point that out.
Here's the scenario:
R1 is connected to an ISP that's policing traffic at 128kbps. 32kbps of
traffic is considered mission-critical and should always get priority
treatment.
R1's config
class-map MISSION-CRITICAL
match access-group name MISSION-CRITICAL
class-map NON-CRITICAL
match access-group NON-CRITICAL
policy-map COMPARE
class MISSION-CRITICAL
priority 32
class NON-CRITICAL
<action 1, 2 or 3>
service-policy output COMPARE
Action 1 = bandwidth 64
Action 2 = shape 64
Action 3 = police 64
Since the ISP is policing at 128 and by default, 25% of the link's
bandwidth
is reserved for the class class-default traffic, the total that the
other
classes can reserve and use is 96k.
Behavior when MISSION-CRITICAL traffic is using 32k continuously.
For bandwidth 64, NON-CRITICAL traffic over 64k is dropped.
For shape 64, traffic in excess of 64k is held in shaping queue unless
the
shaping fills-up, in which case, it's dropped.
For police 64, traffic in excess of 64k is dropped regardless of what
action
is specified for exceed or violate. Even if the action for traffic
exceeding
contract is to remark dscp and transmit, since there's no other
available
bandwidth, the traffic will be dropped.
Behavior when the MISSION-CRITICAL traffic is NOT using the 32k reserved
for
it.
For bandwidth 64, NON-CRITICAL traffic over 64k can "overflow" and use
the
unused bandwidth reserved for MISSION-CRITICAL traffic.
For shape 64, the behavior doesn't change from before ie NON-CRITICAL
can NOT
"overflow" and use any of the unused priority bandwidth.
For police 64, NON-CRITICAL traffic can burst over 64k up to Be and thus
overflow and use some of the unused priority bandwidth.
I assume the bandwidth reserved for the class-default traffic can NOT be
encroached upon but I'm not 100% sure about that.
If anyone disagrees with anything I've said, please let me know. Thanks
Tim
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