End-to-End configuration in Qos

[wfqk]

Hi, We need to End-to-End configuration in Qos sometimes. Anyone can explain or confirm the below?

Here is topology: 

Phone1---router1---router2---router3---phone2

1. End-to-End configuration means all these devices need to have the same configuration for specific traffic, right? 

2. if router2 and its connections to router1 and router2 are very fast, do we still configure router2? 

Thank you

[Wayne DeNardi · Accepted solution]

1. Yes - end to end, means along the whole path, including the two ends, not just the routers

2. Yes - QoS should be configured everywhere, as bandwidth can peak, even for just a fraction of a second, and cause issues.

I'd suggest you have a good read through the Enterprise QoS Solution Reference Network Design Guide.

[wfqk]

Thank you for the good explanation and link

[wfqk]

One more question, if we configure all devices except router2, what could happen?

Thank you

[Wayne DeNardi · Accepted solution]

Router 2 would not priorise any packets, and if there was any congestion, your important packets could get dropped.  If Router 2 is not set to trust or pass the packet markings, the markings can also get lost and not get to the other routers in the traffic flow, and therefore the traffic may not be marked appropriately when it hits those devices, and therefore, end up in a different queue and, again, be dropped if there is any congestion.

[wfqk]

Very good explanation!