From: Douglas M Todd, Jr (dtodd@PARTNERS.ORG)
Date: Thu Jun 21 2007 - 13:08:33 ART
My 2c:
Well -
Basically, I don't like to see drops at all, tail, output, input etc.
This means there is an design flaw or a bandwidth inequality. However,
life is never perfect and drops are a part of the network and a necessity.
Whether you call it Tail, Queue full drop, undiscriminating drop?
Depends on how you view the queuing on the device. When you look at FIFO
a tail drop is pretty specific. Undiscriminating drop is pretty vague
(even though it's implied that all traffic is viewed equally) to me
because it does not imply any queuing/drop mechanism. Undiscriminating
drop would lead me to believe that the device will indiscriminately drop
any packet in the queue regardless of it's position and protocol type,
even packet's in the queue. This is not the case with a tail drop where
a router/switch with full queue will start dropping the packets trying
to enter the queue, but not packets already in the queue.
I think the goal is to understand the queuing on a device and what
happens when the queue fills up to the point of dropping traffic. The
industry states tail drop (meaning it's not just a Cisco thing, but its
also a tcp thing), however, if you understand it better by referencing
it as an "undiscriminating drop" then you are one step closer to fully
understanding and remembering how queuing works on a device. You just
need to remember to yourself that "Tail Drop" or Weighted Tail Drop
means undiscriminating drop or wighted undiscriminating drop.
Either way, is if you understand it, then great!
DMT
johngibson1541@yahoo.com wrote:
> I know these 2 are technically the same.
>
> We don't like that to happen.
>
> But I just think saying "undiscriminating drop"
> is much more specific, to the point.
>
> Every time I see or hear "tail drop", I have to
> translate it to "undiscriminating drop" to
> make sense to myself.
>
> "tail drop" is the physical appearance and can
> happen in different setting and mean different
> things.
>
> "undiscriminating drop" is just plain straight
> forward that we want to prevent.
>
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