[Asterisk-Users] QOS / Cisco / Asterisk

[rsenykoff at harrislogic.com]

<snip>
> We're trying to PQ (Priority Queue) packets on a Cisco using ACL's. What
> we're trying to avoid is hardcoding the IP address in the ACL. We were
> trying to match by TOS set by Asterisk however it seems we've run into a
> snag where the packet TOS tends to get reset somewhere on our network.
> Has anyone had this issue? We're running Cisco everywhere inbetween
> (even the switches). Is there an alternative way to match these? We've
> thought of by port but that's kind of ad-hoc IMHO.

If the TOS is getting reset somewhere out there you need to go through
all of your switches and make sure that none of them are messing with
the TOS.  Unfortunately doing QOS on Cisco switches is a black art as
the necessary commands depend on the hardware and the IOS version (or
CatOS version if you are unlucky).  Check the documentation for your
switches for the "mls qos trust" command.

Cisco routers, on the other hand, don't mess with IP TOS/DSCP labels
unless you specifically ask them to.
</snip>

What's wrong with doing it by port? If it is possible that something else 
out there may use the same TOS flags as Asterisk, by prioritizing port 
4569 (IAX2 protocol) you know for sure that the only packets in that queue 
are VoIP traffic. Also, what about your incoming traffic? Are the TOS 
flags correct there? I'm not saying that TOS is bad, just that as you've 
seen, it can get changed along the way. I'm using port number to separate 
traffic and it is working great.

-Ron
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