[cisco-bba] PPPoE and QOS for voice traffic

[Benoit GRANGE]

Eric,

> In a PPPoE environment, can QOS aware Layer 2 devices "see" 
> the TOS or 
> DiffServ if it is set in the IP packets? Or will it just see 
> the traffic 
> as Layer 2 traffic and be totally blind of anything IP 
> contained within 
> the PPPoE encapsulation?

in most layer 2 Ethernet switches the switch may prioritize trafic based on the 802.1p COS field of the Ethernet frame. If the switch is layer 3 aware (IP), then the switch may also look in the TOS or DSCP field of the IP packet *if* the IP packet is directly contained in the Ethernet frame.

Because you use PPPoE, the IP packet is encapsulated to "deep" in the frame and you may not be able to do that, at least not on current Cisco boxes.

> If this cannot be done, what methods are available to 
> prioritize traffic in a PPPoE environment. Specifically, we use DSL and Wireless 
> with PPPoE for customers.

You may copy the TOS field of the IP packet in the COS field of the 802.1p Ethernet frame (this must be done on your PPPoE router), and then prioritise based on the COS field

Benoît