QOS on internet facing router

[carl_townshend]

Hi All

We are having some issues with audio/video such as webex over the internet.

We have a 500Mbit circuit coming in which can get very busy during times.

We have frequent audio/video drop outs due to the congestion, it is generally in the download direction.

I know there is nothing you can do once on the internet with qos, is there any way I can control this at least coming in to me, or would it need to happen further upstream and so I have no control?

My plan was to put a qos policy on the inside interface of the internet router facing us, and on the outbound direction i.e coming towards us, this would control the download side.

Or will it not work as it needs to be controlled further upstream?

cheers

[Georg Pauwen]

Hello,

you can certainly configure a QoS policy on the outside interface. Here is a generic one (WebEx uses 443 as far as I know, the policy example assumes that voice and video traffic are marked with DSCP 46 and 34, respectively). Which router model (e.g. 4331) do you have ?

class-map match-any VOICE_VIDEO_CLASS

match dscp 46

match dscp 34

!

policy-map VOICE_VIDEO_POLICY

class VOICE_VIDEO_CLASS

priority percent 30

class class-default

fair-queue

!

interface GigabitEthernet0/0

service-policy VOICE_VIDEO_POLICY out

[carl_townshend]

Hi George

As the congestion is mainly coming on the inbound direction to the outside interface, the router then pushes this to our firewall on its inside interface.

Am I best applying it on the inside interface on the outbound direction?

Do you think the ISP will honour the markings and not strip them also?

cheers

[Georg Pauwen]

Hello,

you have no control over what the ISP does, most likely they do nothing with your markings. All you have control over is your own outside interface. Try and apply the policy inbound and check if the congestion decreases...

[carl_townshend]

Hi George

So apply it inbound on the outside interface that connects to the ISP?

Can you apply the priority queue inbound ?

[Georg Pauwen]

Hello,

what router model and IOS version do you have ? Try and apply the policy, if the IOS complains, it will tell you which part it doesn't like...

[carl_townshend]

Hi George

It is an ISR 4551 router

[Georg Pauwen]

Hello,

in this case, I would suggest either the 'priority level 1' or 'shape average percent 50' commands:

policy-map VOICE_VIDEO_POLICY
class VOICE_VIDEO_CLASS
shape average percent 50

or
priority level 1
class class-default
fair-queue

[paul driver]

Hello

---

@carl_townshend wrote:

Hi All

We are having some issues with audio/video such as webex over the internet.

We have a 500Mbit circuit coming in which can get very busy during times.

We have frequent audio/video drop outs due to the congestion, it is generally in the download direction.

I know there is nothing you can do once on the internet with qos, is there any way I can control this at least coming in to me, or would it need to happen further upstream and so I have no control?

My plan was to put a qos policy on the inside interface of the internet router facing us, and on the outbound direction i.e coming towards us, this would control the download side.

Or will it not work as it needs to be controlled further upstream?

cheers

---

If you have a congested wan link then depending how often this is qos would only be temporary solution you may eventually need to increase it , But your right once traffic has hit your wan interface ingress it has already traversed the wan  link so not much really you can do from your end.

However you can negotiate with you isp what CIR you have and shape accordingly to that, Is it possible the other end of your wan link has a higher CIR then you do? -  If so they may be overwhelming the connection towards you (egress blocking) so also possibly check that and if so ask them to shape to your CIR.

[carl_townshend]

Hi

You are right, I think it could be the CPE Adva access equipment dropping the traffic at our site as I am sure the bandwidths are set there or further upstream

Would you still put the QOS policy on the internet router?

As I said before, is it best to apply it on the inside interface "our side" of the internet router and apply it outbound towards our LAN?

I believe you cannot assign a priority queue inbound on an interface anyway

Also, would it be worth applying the policy on both interfaces on the router?

[Joseph W. Doherty]

If the congestion is WAN ingress, ideally you would want to assign QoS on the ISP's egress to you (which almost all ISPs will not do - you might ask, though, whether you could insert you own router between the ISP's and your link, on their side, which would allow you to manage link congestion with QoS).

What you can do on your router (at your site), you can police bandwidth hogging ingress traffic at some rate leaving bandwidth available for your A/V traffic. This, though, runs into problems if the bandwidth hogging ingress traffic doesn't slow when it detects drops and often the ingress traffic can be slow to respond to the drops (meaning to be effective you need to police that traffic very harshly). And/or if the bandwidth hogging ingress traffic is TCP based you can shape the outbound ACKs to control how fast you receive that traffic. This too has the problem it tends to be inexact and you need to shape very harshly. (NB: I've used both, they work, but you effectively lose a lot of you ingress bandwidth to insure there always excess bandwidth for your A/V.)

What you can also consider is obtaining a 3rd party traffic shaping appliance. These do things like TCP ACK shaping (much more precisely) and they also do things like spoof RWINs to control external TCP sending rates. (NB: These devices are about as good as it gets managing ingress bandwidth.)

As the others have mentioned, there could be some benefit to having an egress QoS policy (i.e. if you have occasional egress congestion that's adverse to your A/V applications).

Others have suggested you might need more bandwidth, perhaps, but another alternative to that would be a different WAN link dedicated to just your A/V traffic. There's always risk, w/o QoS, to mixing bandwidth hogging traffic on the same link with latency/jitter sensitive traffic.

[ZK916]

This is an outdated post but it is relevant to an issue one of my customers is facing. 

My understanding is that QoS has no effect to the egress traffic flowing from the customer's router to the Internet (ISP's PE or router), would that be a correct statement? 

Thanks in advance. 

~zK 

[Joseph W. Doherty]

No, it's correct, insufficient information, because answer depends on QoS policy, volume of traffic and applications being used.