From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Tue May 04 2004 - 18:48:18 GMT-3
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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