[e2e] Extracting No. of packets or bytes in a router buffer
fred at cisco.com
Thu Dec 14 13:26:27 PST 2006
On Dec 14, 2006, at 12:05 PM, Alexandre Grojsgold wrote:
> Of course, it´s ephemeral.
I point that out because it is a fundamental criterion that the SNMP
community has been using for a while. It is one thing to enable an
NMS to read the configuration of a device (largely static) or read a
counter (monotonically increasing, so that subsequent reads tell you
what happened between the reads). ifOutQLen is a gauge, which is to
say that it looks a lot like a random number in this context. In such
a case, the SNMP community will generally suggest that the number is
not all that meaningful.
> I am really impressed to know it is so difficult to grab this kind
> of information, since router manufacturers claim they can do magic
> with queue managing, like diffser, traffic shaping, priority
> queueing, etc... all of this looking at the queues and making
> tricks with them.
Do I detect a note of sarcasm?
The point is what is known by whom at a particular time. A bit of
code looking at a choice of queuing something locally or handing it
to the next widget makes a pretty simple determination - when it
tries to hand the datagram off the next widget accepts it or not, and
if not, it does the local thing. "accepts" can have various meanings
- it may actively reject it, or (more probably) has given permission
to send some quantum and the quantum is used up. Looking at
individual queues, one can do a lot of things such as you mention.
The hard part is in a distributed system (a system that has
functionality on a variety of cards managed by a variety of
communicating processes) to have a single overall view of the entire
state of the process at exactly the time one wants to find the answer
to the overall question.
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