Unanswered Question
Jun 2nd, 2008
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On my edge routers I have setup traffic classification on the LAN ports and queuing and prioritization on the output (WAN) ports. My question is what do I do on my distribution and core routers to obtain end to end prioritization? We use a lot of video conferencing (tandberg) and some VOIP.

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Wilson Samuel Mon, 06/02/2008 - 05:41
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As far as Cisco standard practice is concerned, they higly recommend that:

1. Classification and Marking should take place at the Access Layer/End Device

2.Congestion Management and Congestion Avoidance should be implemented at the intermediate devices as and when required.

Please let us know if you want further info on the point and it shall be our pleasure to do so.

Kind Regards,

Wilson Samuel

tomredmond Mon, 06/02/2008 - 06:04
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if you have links/advice on point 2 I would be grateful.


Tom Redmond

shiva_ial Mon, 06/02/2008 - 06:32
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in simple way

assuming on lan ethernet interface which is incoming to the router you will mark the packet with some DSCP value and we have to define output policy on serial interface which may be the output interface so the marked packet get priortised

following linkf shows configuring qos


post if you are not clear

rate if it helps


Joseph W. Doherty Mon, 06/02/2008 - 16:54
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In principle, similar to your WAN QoS which is likely priority queuing for your real-time traffic, i.e. VoIP and vidconf. However, in practice, the two differences usually are LAN routers (L3 switches?) are not as QoS feature rich as software routers, and for pure L2 switches, instead of QoS, you'll likely need to work with CoS (802.1p), if it's supported.

For L3 switches, place the packets with the real-time ToS, usually DSCP EF or IP Precedence 5, into either the switch's version of a priority queue (on Cisco switches sometimes known as the expedited queue). At L3, by default, ToS is usually left alone, although you need to configure to process it.

For L2 switches, map your L3 ToS into a L2 CoS (802.1p) that will denote real-time traffic (perhaps value 5). Usually this mapping of ToS to CoS is supported on a multilayer switch (a simple map would be IP Precedence directly to CoS). Each pure L2 switch, assuming they understand CoS, will then need to "trust" the ingress CoS value, queue/treat it as best as possible on the platform, and pass the CoS value along to the next L2 switch.


On Cisco LAN devices, you might investigate whether yours support Auto-QoS, and whether it would be sufficiently suitable. Even the first gen of Auto-QoS targeted real-time like VoIP.


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