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As part of some product testing that I am doing, I am sending traffice
between two end nodes where the some of the traffic has the
Minimize-delay TOS bit set and some has the Maximize-throughput bit
set. If I sniff the packets on the originating side, the IP header is
what I expect. However on the other end (after passing through a 3550
switch) I see that the TOS bits have all been reset to 0x00.

Is this normal operation? Is there a way to disable this?

TIA!

In article < om>,
<foldingwidgets-> wrote:
:As part of some product testing that I am doing, I am sending traffice
:between two end nodes where the some of the traffic has the
:Minimize-delay TOS bit set and some has the Maximize-throughput bit
:set. If I sniff the packets on the originating side, the IP header is
:what I expect. However on the other end (after passing through a 3550
:switch) I see that the TOS bits have all been reset to 0x00.

:Is this normal operation? Is there a way to disable this?

As I recall, the TOS bits are one of the criteria used for QoS
classification on the 3550. The output 0x00 could represent the
result of QoS -- that is, everything is likely being mapped to the
same default priority.

I have read a little about QoS but never played with it, so I do not
know whether this could be disabled. -Possibly- there is a method
involving mapping the various interesting ToS bits into the corresponding
binary-number priority. But the 3550 does not have 8 different
output queues, so you might be forced to map more than one point to
the same output ToS I guess. (The 3750 has a greater number of
output queues if I recall correctly.)

--
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they see in .signatures.

<foldingwidgets-> wrote in message
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> As part of some product testing that I am doing, I am sending traffice
> between two end nodes where the some of the traffic has the
> Minimize-delay TOS bit set and some has the Maximize-throughput bit
> set. If I sniff the packets on the originating side, the IP header is
> what I expect. However on the other end (after passing through a 3550
> switch) I see that the TOS bits have all been reset to 0x00.
>
> Is this normal operation? Is there a way to disable this?
>
> TIA!
>

It is normal. By default, your equipment will not accept incoming QOS - for
good reason. On the incoming interface type:

mls qos trust cos

that will tell the interface that your equipment trusts the QOS coming in.

Hope that helps,

Jim

Thank you so much! (I actually had to use "mls qos trust cos
pass-through dscp").