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stealth
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QOS configuration on Cisco 3750 L3 switches

Mon May 28, 2012 7:51 am

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??

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mellowd
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Re: QOS configuration on Cisco 3750 L3 switches

Mon May 28, 2012 9:21 am

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

stealth
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Re: QOS configuration on Cisco 3750 L3 switches

Mon May 28, 2012 9:28 am

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



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

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

Any advice to a QOS beginner?

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raven
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 4:02 am

I like Daniels (reaper) post about this topic: http://lostintransit.se/2012/03/07/catalyst-qos/
http://ccie20728.wordpress.com/

stealth
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 5:40 am

Thanks, I'll have a look now.

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matgar
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 9:00 am

Just dont forget to actually turn on QOS.

Code: Select all
mls qos

stealth
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 10:42 am

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

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mellowd
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 11:00 am

Auto-QoS

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ristau5741
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 11:08 am

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.
Tips of the day:
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stealth
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 3:17 pm

ristau5741 wrote: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.



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.

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mellowd
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 4:23 pm

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

Langly
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Re: QOS configuration on Cisco 3750 L3 switches

Tue May 29, 2012 4:53 pm

ristau5741 wrote: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.



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

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ristau5741
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Re: QOS configuration on Cisco 3750 L3 switches

Wed May 30, 2012 7:43 am

Langly wrote:
ristau5741 wrote: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.



++ 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.
Tips of the day:
- The human mind is the ultimate creation invention.
- I have so many customers, my customers have customers.
- Sausage time
- POP, stack, and store

Langly
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Re: QOS configuration on Cisco 3750 L3 switches

Wed May 30, 2012 12:09 pm

ristau5741 wrote:
Langly wrote:
ristau5741 wrote: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.



++ 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.


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

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DanC
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QOS configuration on Cisco 3750 L3 switches

Wed May 30, 2012 12:46 pm

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


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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ristau5741
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Re: QOS configuration on Cisco 3750 L3 switches

Wed May 30, 2012 2:47 pm

[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.
Tips of the day:
- The human mind is the ultimate creation invention.
- I have so many customers, my customers have customers.
- Sausage time
- POP, stack, and store

stealth
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Re: QOS configuration on Cisco 3750 L3 switches

Wed May 30, 2012 3:34 pm

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?

'

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