Patrick D wrote:
>
> On the Hp site, I found a question explaining the impact of setting
> a QoS flag on Cisco routers preventing the HP3000 ( MpeiX 6.0) to
> communicate out the local network and the way to resolve it with
> the NSTGDB0/NSTGDK3A patch
>
> I applied the patch and the HP3000 is now ok
>
> But I want to find again this question ( for explainations) and I
> don't find it ?

The "problem" arises from newer switch/routing technologies using the
DSCP (Differentiated Service Control Protocol) method of QoS versus
the older TOS flag bits (IP precedence).

The original RFC requires that the IP precedence bits cannot change
for the duration of a connection; DSCP says that it can be changed.
The older RFC says if it changes, you reset the connection.

The original question as posted to the list can be found at:

   http://raven.utc.edu/cgi-bin/WA.EXE?A2=ind0211B&L=hp3000-l&P=R3599

The details of the problem are outlined in RFC2873:

   http://www.faqs.org/rfcs/rfc2873.html

The "fix" proposed in RFC2873 is to have the TCP stacks on client and
server to *ignore* precedence bits and leave that to intermediate hops
(routers and/or switches).

I presume the "patch" just disables precedence checking.

This shouldn't bite anyone unexpectedly unless you are playing with
the newer QoS (DiffServ/DSCP) capabilities in your network, such as
is most often seen these days with IP telephony (where QoS becomes a
PITA [Pain In The Arse]) :-)

Jeff

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