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Author Topic: QoS on the LAN - setting up low-priority downloads  (Read 518 times)

Weaver

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QoS on the LAN - setting up low-priority downloads
« on: December 19, 2016, 07:16:04 AM »

My question: Is it possible to make certain downloads lower priority compared with users' manual web browsing (assuming the question of how to categorise and identify the traffic is solved somehow, a separate problem), obviously without having access to the servers that are the source of the data?

And I don't mean simply rate-limiting certain classes of traffic either, in the absence of higher priority traffic then the lower priority downloads need to run at full speed.
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Chrysalis

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Re: QoS on the LAN - setting up low-priority downloads
« Reply #1 on: December 19, 2016, 08:48:13 AM »

Is 3 main ways you can do this.

prioritise per device - easy
prioritise per src/dest ports - easy
prioritising per specific service - hard

the 3rd option e.g. either requires DPI and knowing how to identify specific traffic and/or knowing src/dest ip's for specific services, given the large amount of CDN usage these days and massive clusters of ip's services use, classifying without DPI would be very difficult.

tomato firmware has traffic classification QoS stuff, but when I played with it, it was not very good, although better than nothing I guess.

Asus routers have some kind of automated QoS available on new firmwares/devices but I dont know exactly how it works.

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Weaver

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Re: QoS on the LAN - setting up low-priority downloads
« Reply #2 on: December 19, 2016, 08:52:04 AM »

Leaving aside the traffic classification problem for the moment, how could prioritisation itself be make to happen?
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aesmith

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Re: QoS on the LAN - setting up low-priority downloads
« Reply #3 on: December 19, 2016, 04:24:37 PM »

When you say "on the LAN" do you mean within your Ethernet network?   To make that work you would need to rate limit the LAN interface to slightly lower than the Internet download speed, otherwise any prioritisation won't "see" any congestion and therefore any need to prioritise.

For the details of how to do this, it's product specific.   On  Cisco router's LAN interface ..
- Create class definition that matches everything except your low priority download (named for example "NOT-LOW")
- Apply overall traffic shaping policy to the LAN interface
- Apply nested policy within that overall shaping to reserve certain bandwidth for the NOT-LOW class

If you don't have the overall traffic shaping your router is going to see for example 6 meg of download of which 4meg is low priority, however the LAN is 100meg (or Gig) so the router sees no reason not to transmit it all.

This is assuming TCP traffic, meaning that the low priority streams will slow down once you start dropping.
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boost

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Re: QoS on the LAN - setting up low-priority downloads
« Reply #4 on: January 16, 2017, 11:30:01 AM »

Hi Weaver

I would recommend you have a squint at DSCP marking your traffic and then policing based on the markings or something.

Windows 7 has the ability to mark traffic by itself (I used to slap DSCP46 / Expedited Forwarding / Voice) on my gaming traffic so I imagine all operating systems have the ability in some form.

Next, you'll need a router or L3 switch capable of examing the DSCP markings. I'm no expert but typically, one define a 'Priority Queue' that has absolute highest priority but very little actual bandwidth assigned to it. Tiny UDP packets, typically, voice, gaming traffic, etc.

Then, you have another 3~ queues for 'other' stuff at varying levels of priority. Cisco does all this quite easily but I bet there's loads of ways to achieve it.

Cisco has terms like 'WTD' or weighted tail drop, 'SRR' or Shared Round Robin.

Hope some of this helps :)

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Weaver

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Re: QoS on the LAN - setting up low-priority downloads
« Reply #5 on: January 16, 2017, 12:54:37 PM »

@boost - thanks for that !

I'm in the market for a better switch so I'll take that into account.
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