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QoS question

Unanswered Question

Hi,


I have a router with 2 T1s going to the one ISP, and I am doing per-destination load-balancing on these 2 T1 lines. I am about to get a 3rd T1 with a different ISP. All 3 T1s are on one router. The 1st 2 T1 are used for internet browsing from and to the internal network, and the 3rd T1 will be mainly used for bulk smtp and ftp from the internal network to the internet. However, I want to use this 3rd T1 for outgoing http when it’s not heavily used, but I want to make sure that when the 3rd T1 is becoming heavily used due the bulk smtp/ftp (let’s say 80% of the max bandwidth) the router will no longer send outgoing http down the 3rd T1. I am pretty sure that with QoS I should be able to do that, but I need help to put me on the track to get this configured.


Thanks for the help.


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Georg Pauwen Fri, 09/30/2005 - 10:19
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    2017 WAN

Hello,


your QoS could look like this:


ip cef

!

class-map match-all HTTP

match protocol http

!

class-map match-any SMTP_FTP

match protocol smtp

match protocol ftp

!

policy-map INTERNET

class HTTP

bandwidth percent 100

!

policy-map OTHER_BULK

class SMTP_FTP

bandwidth percent 80


Then, apply policy map INTERNET to the T1s you are using for the Internet, and policy map OTHER_BULK to the 3rd T1.

The idea is that, in case of congestion, the first T1s will be used exclusively for HTTP traffic, and 80% of SMTP and FTP traffic will always flow through the 3rd T1.

Can you try that and see if that works for you ?


Regards,


GP

Thanks for the reply. Just to make sure. . . Will the above configuration stop traffic not defined in the SMTP_FTP class map to go down the 3rd T1 once the line reaches the 80% threshold, or will it still allow other traffic type to go through while guarantying 80% of the line to the SMTP_FTP during contention? You are correct in assuring that the 3rd T1 should be guaranteed 80% of the line, but I am not sure if the above configuration will make sure that when the bandwidth on the 3rd T1 reaches 80% usage (due to the SMTP_FTP) that it will no longer allow other traffic (other than the SMTP_FTP class map) type to go through.

The reason for this is that I don’t mind much if the SMTP_FTP traffic is on a maxed out T1 line, but I know our users will go nuts if they are browsing off a T1 near 95% of max capacity.


Thanks again for the help.


Georg Pauwen Fri, 09/30/2005 - 12:02
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    2017 WAN

Hello,


the entire CBWFQ configuration will only become effective when there is congestion, if there is none, all traffic will flow through all links, which should not be a problem. 80% of the 3rd T1 will be guaranteed for SMTP and/or FTP traffic, the remaining 20% will be available for other traffic. So, when there is congestion, 80% will be used for SMTP/FTP, and only 20% for HTTP.

Does that make sense ?


Regards,


GP

Thanks for the reply, and I am sorry because I don’t think I made myself clear. What I meant to say is that when the 3rd T1 reaches 80% of its max capacity due to the SMTP_FTP traffic I do not want other traffic (i.e outgoing http and others) to use the 3rd T1 as it will experience poor quality due to the contention on the line. In other words, when the line is not heavily used, it is ok to have outgoing http, but when it starts to become congested then only allow the SMTP_FTP and block other type of traffic to use this line. I guess it is more of policy based routing question than strict QoS.


Thanks again for the help

attrgautam Fri, 09/30/2005 - 20:40
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Instead of using CBWFQ, use priority queuing on the link, LLQ will brutally drop all the other traffic. That should solve your issue.

policy-map SMTP

class SMTP

priority 2048

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