Just a general questoin about applying QoS mechanisims to an ethernet ISP Link...
General Scenarios: I have a Cisco 2811 and i want to apply LLQ for all sip traffic outbond towards the internet.
1. If my ethernet link speed is 100Mb and my ISPs bandwidth to my link is 1Mb/1MB, how exactly do i give the bandwidth command? Is it based on the 100 Mb or the 1 Mb?
2. Must i apply the bandwidth 1000 to the ethernet interface for LLQ to work correctly?
Any opinions or real world experience of this would be great.
Thanks & Regards
You should use the policy on the interface that connects to the ISP so any priority traffic is prioritised before it hits the ISP. Unless you have some kind of Service Level Agreement (SLA) , they won't have a clue about your particular traffic types, they only thing they normally do is police your access rate in case your exceed the purchased CIR. Never assume they will give your voice traffic over anything else. By shaping on your egress interface, you ensure two things -
1) The traffic passed to the ISP is already prioritised. The ISP will (hopefully) pass this first in , first out so your voice traffic will always be in front of the queue at the destination.
2) Because you have shaped to the purchased CIR (1Meg) on the egress interface, the ISP should never drop your traffic. If you were to exceed the CIR, the ISP would not differentiate between the more important voice/signalling traffic and the other data traffic - they drop anything over the CIR. So this improves reliability for the voice traffic.