From: Devi Mallampalli (Devi.Mallampalli@chubb.com.au)
Date: Wed May 05 2004 - 00:02:23 GMT-3
Hi Ken,
I totally agree with Howard on not muck around with higher system
precedence values for data traffic types in production networks. But I
do aware that your intention is only theoretical.
Now coming back to your question, I would retag the remaining traffic.
The basis of my thinking is when you put the rest of the traffic types
in the a best effort/default class of class-default, there will be
indiscriminate drops if the congestion hits the wire. Where as if I
"retag" the remaining traffic types (other than my "high" priority
traffic) with an appropriate or suitable DSCP code values, I can be
certain about the "DROP PROBABILITY" and well aware on what kind of
traffic type packets will be dropped in the event of congestion. In
other words I can influence and afford to loose ( or get dropped) some
of my users "web browsing" packets rather than Telnet packets at the
peak hour traffic even though my high priority traffic is some thing
else ( for example RTP & RTCP).And unless you go beyond the idea of
"bundling the remaining traffic types" to gether , you can not meet
greater granularity and control and influence the 2nd and 3rd priority
traffic transmission. But again I am speaking from production networks
point of view and that too from own experience point of view.
In the back ground of today's complex corporate networks , I am an
advocate of "end to end" Qos solution , both layer 2 and Layer 3. Which
also means , knowing and controlling the transmission of every Layer 4
packet types those are moving on your wire and assign them respective
importance and affordability to get dropped in the event of a
congestion.
Regards
Devi.
-----Original Message-----
From: Kenneth Wygand [mailto:KWygand@customonline.com]
Sent: Wednesday, 5 May 2004 11:54 AM
To: Howard C. Berkowitz; ccielab@groupstudy.com
Subject: RE: Best Effort Definition
Howard,
Thank you for your complete and very comprehensive analysis. My
question, however, was theoretical in application and is not intended
for a production environment. Technically the bits in the TOS field can
be set to anything provided they support the overall implementation of
the network policy in effect. The real basis of my question was if a
question says "set a specific priority or DSCP for a specific type or
subset of traffic and use "best effort" for everything else", do I retag
all other traffic with all zero's for the TOS byte or do I trust them
the values of the TOS byte for this traffic. What does "best effort"
actually imply, all zero's or unchanged?
Thanks,
Ken
-----Original Message-----
From: nobody@groupstudy.com on behalf of Howard C. Berkowitz
Sent: Tue 5/4/2004 5:48 PM
To: ccielab@groupstudy.com
Cc:
Subject: Re: Best Effort Definition
At 4:31 PM -0400 5/4/04, Kenneth Wygand wrote:
>Hello Group,
>
>
>
>I think I know the answer to this one but I just want to get
some more
>opinions...
>
>
>
>If I am performing QoS (whether it be CoS, IP Precedence, ToS
Bits, or
>DSCP), supposed I would like to "mark all traffic going from
router A to
>router B as IP Precedence 6 while other traffic receiving "best
effort"
>service"... obviously through some kind of classification,
marking and
>queuing I would make sure all traffic from router A to router B
receives
>the type of service it requires.
Why are you using priority 6? Priority 5 is intended as the
highest
to be used for application traffic.
>However, what about all other traffic?
Priorities 6 and 7 are reserved for time-criticall routing
protocols,
network management, etc. Never interfere with the priorities
for
these services, or you may create a situation where the routers
lock
up and you cannot get control. Along the same lines, you might
want
to create fine-grained rules to have telnet from a control
console at
priority 5.
>When requesting that other traffic gets "best effort", should
one leave
>the QoS markings as-is, or actually remark them back to all
0's?
Leave them as-is. I can't say with certainty that any other
applications will set priority, but they rarely do without a
good
reason. If, for example, you use TFTP to reload NVRAM during
production hours, I might give it priority 4.
To put it in perspective, the original military purposes of the
precedences were having the highest for network and internetwork
control. The next was used, among other things, for Emergency
Command
Precedence, which is an order to launch a nuclear weapon.
Considering
that the sender of such a message may become part of a mushroom
cloud
at any time, that message HAS to take priority -- but even then,
the
network/internetwork control had even higher precedence, because
if
they weren't working, the network might not be there to carry
the
Emergency Action Message at ECP precedence.
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