QoS question about input/output traffic relationship on the same interface

Unanswered Question
Sep 10th, 2008


I am just getting to know QoS (on routers) properly, and I have one dilemma to solve.

Let's say we have a QoS policy applied to the router's WAN interface, in outbound direction. This is some serial link, for instance. We marked the traffic, and gave it some bandwidth - let's say 50% of the link.

So, in the case of a congestion, the marked traffic should always get 50% of the BW.

the Q: what will happen if heavy traffic starts coming in from the WAN link i.e. in the inbound direction of that same interface? Will that outbound QoS policy matter at all? Does IOS know how to check the receiving traffic also, in order to maintain desired BW set in the QoS policy? I mean, that WAN traffic is coming at full speed in the very same interface (in which I tried to reserve some BW in the output direction) and my guess it doesn't care about my policy. It just hits hard on my router - or am I missing something?

The solution would be to enforce the similar QoS policy on the neighbor router, but I just can't do that. The configuration of the network is complicated and it would be a major pain setting up QoS on the other side of that WAN link.

Basically, I need to reserve some BW for video surveillance traffic, but at the same time not to overload the WAN link. The easy way is to do a one-way QoS and reserve the BW in the out direction on the WAN interface. But is it enough? What about the incoming traffic from the WAN?

Thanks a lot

I have this problem too.
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Marwan ALshawi Wed, 09/10/2008 - 18:34

Hi Bojan

good and interesting question

so inrespons to this question each port has its transmit and recieve queues this apply to router and switch

and there is droping throushoulds as well

once the traffic go above the limit i mean all traffic types the port will start droping with WRED wighted random detect the droping will be DSCP based for example the bulck data will be drop befor voice and so on

and about the incoming and outgoing bandwith

for end to end Qos u need to configure on ly the outgoing direction for bandwidth managment and allocation while the the incoming direction used for mark and reclassify traffic to be match on the other end with outboungd direction on the same box

like inboundclissify--router--outbound bandwidth allocation---WAN--inbound remark--router--outbound (maybe policing going to lan)

and vis versa

good luck

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