Hello, I'm after some advice on QOS for our Siemens VOIP phones.

We have PC's that connect through the Siemens IP phones and back to the cisco 3750 which is connected to our core 6500 via L3. The phones use a voice VLAN and the PC's use another VLAN. The whole setup seems to work ok but I was just wondering if the QOS was configured correctly. Our current config on our 3750 switches are mls qos trust dscp on the port that connects to the phone and PC and mls qos trust dscp on the L3 links. The phones are configured for "QOS L2/L3"

From the reading I've done so far it seems that any ports connected to a L2 device should be set to cos and not dscp?


I don’t really understand QOS and it's such a huge subject I haven’t got time to dedicate towards at the moment. Could anybody give me some pointers..... I was expecting to see something that tells the switch to prioritise certain traffic or is it done on port??

If you don't understand QoS, I would recommend using AutoQoS on the switches

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www.mellowd.co.uk/ccie/

Maybe I should say I understand the concepts of QOS but not autoQOS then

I'm following on from a config set by previous boss....

Any advice to a QOS beginner?

I like Daniels (reaper) post about this topic: http://lostintransit.se/2012/03/07/catalyst-qos/

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http://ccie20728.wordpress.com/

Thanks, I'll have a look now.

Just dont forget to actually turn on QOS.

Blimey, the QoS topic is huge... I may just leave it for now as we've not had any issues. I was just curious as to how it should work or if it is working! I stupidly thought that somebody would say, "configure L2 ports for COS and L3 ports for DSCP and job done"

Maybe I need to hit some more advanced Cisco courses.


Cheers

Auto-QoS

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www.mellowd.co.uk/ccie/

BTW, you don't want to run QoS on the 3750 series, they are notorious for small buffers,
if you do deploy, you will run into lots of dropped packets due to insufficient buffers.

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"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

OK, I do remember reading about the small buffer sizes on the 3750 series. Good tip!! So is it an undocumented recommendation that you shouldn't run QoS on 3750 series.

Whether you run QoS or not the buffers are still small.

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www.mellowd.co.uk/ccie/

++ to this, encountered this problem with ours and it does happen

we learned the hard way, were in process of rolling out Video to Desktop via Movi and Lync,
had to roll back the QoS configs, customers were complaining loud about network slowness,
connectivity issues, and such, dropped packets was the cause, when we removed the QoS
everything worked again.

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"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

We had the lovely game of backups failing on our core cause of this. Our 5ks arrive in a couple days to replace the 3750e's we've used for two years

This.

We have 3750's with QoS enabled / configured end to end and we don't have any problems with it.
You have to remember though that these switches are an access layer switch, not distro or core and as such aren't geared up towards bulk data transfer etc.

Ristau - did you try tuning the QoS at all or just turned it off?



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[quote="DanC"]
Ristau - did you try tuning the QoS at all or just turned it off?


TAC case was opened, buffers tuned, thats when we learned about the issue.
at the time it was quite undocumented and unadvertised. then we just turned it off
or I should say unconfigured about 200 switches.

_________________
"If you're good at anticipating the human mind. It leaves nothing to chance."
-Jigsaw

So, If I don't want to bother with QoS on my 3750's does that mean that there is no point configuring it on the L3 interfaces of the 6500 switches?