Do we need ISP Qos service?

[wfqk]

Hi, The topology is like this:

data center edge router interface g1/0  --- ISP ---f1/1 branch office router.

If ISP do not provide Qos service, the client needs to configure trust, classification and mark at edge router interface g1/0 and f1/1 for inbound traffic respectively. but most possible congestion is located at these two interfaces. so if we do it like this, the Qos would have less effect, can we say like that? Thank you 

[Reza Sharifi]

Hi,

The ISP usually does not honor any QOS marking or classification from the customers routers. So, say you mark traffic leavving your router with COS 5, the provider equipment will change it to deafult (0).

HTH

[wfqk]

Thank you for your reply. Yes I agree with you.

Question is if ISP provides Qos service, the edge router would get better Qos effect on inbound traffic? because that interface g1/0 and f1/1 are real bottleneck. Do you agree? 

[Reza Sharifi]

Well, if they are low speed connections, than they could be the bottleneck. Usually WAN speed is slower than LAN speed, although WAN speed has increased a lot in the last few years.

HTH

[Joseph W. Doherty]

For QoS purposes, you can "shape" at G1/0 such that traffic sent to F1/1 doesn't exceed F1/1's capacity. If done, then the likely congestion point would be at G1/0. (NB: This also assumes F1/1 doesn't received data from other sources.)

BTW, generally ISP don't support QoS but they also usually don't change ToS values either.

[wfqk]

---- "BTW, generally ISP don't support QoS but they also usually don't change ToS values either."

Do they have trust configuration when traffic go through ISP? If no, all configuration would be lost even if they do not change Tos values, right? 

Thank you

[Joseph W. Doherty]

What configuration would be lost if traffic passes through an ISP? Your configurations, on your equipment, shouldn't be subject to change by an ISP.

The ToS byte, as part of the IP packet header, could be changed by an ISP, but again, they normally wouldn't change it. (If an ISP did change your ToS byte, you could protect it by encrypting your packets. Then the ISP could modify your outer encapsulate packet's ToS, but not the inner encrypted packet's ToS.)

[wfqk]

---“ What configuration would be lost if traffic passes through an ISP? Your configurations, on your equipment, shouldn't be subject to change by an ISP.”

Yes, Tos configuration. but if Tos is not subject to change by ISP, that means these Tos value would remain in the traffic all over the ISP, and also means ISP router should keep trust configuration in ISP each routers, otherwise these value would get to 0 when the traffic go through ISP. Am I right? 

 Thank you again..

[Joseph W. Doherty · Accepted solution]

it's not so much that ISP "trust" ToS, it's rather they just ignore it.

BTW, Cisco routers, and later Cisco switches generally ignore ToS, by default.

[wfqk]

Thank you so much for explanation. 

 Ignoring it by ISP means that ISP usually do nothing on Tos or Qos. So, When the traffic with its Tos goes out from interface g1/0 to ISP, and then enter f1/1 of branch office router, can we say the Tos value do not change after it pass through ISP? if so, we do not need to remark traffic and just use original mark after the traffic enter the edge router, right? 

[Joseph W. Doherty]

Correct - that's usually the case.

[wfqk]

Thank you!