8mbit/s out of 50mbit/s

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Jul 28th, 2010
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Hi,


We just upgraded our leased line from 10mbit/s to 50mbit/s. But can't get the speeds up between two clients.

We are running a Cisco 3745 connected to Cisco 1841 using GRE tunnel.


Tried changing the tcp windows size using iperf.


8k window = 8Mbit/s

16k window = 26Mbit/s

32k window = 28Mbit/s

64k window = 28,5Mbit/s


If i started 10 sessions i can max out the leased line at 48,5Mbit/s so the speed on the line is correct.


Is there something that can be tuned on the routers to get full speed?

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Edison Ortiz Wed, 07/28/2010 - 06:54
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You said 10 sessions max out the line so the routers are providing the speed that you need.

You also said that changing the Windows size provides higher throughput.

I guess you don't realize the problem is at the host and NOT the router, right?

Kevin Brennan Wed, 07/28/2010 - 08:05
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Hi Marcus,


To test raw speed with iPerf you should have it in udp mode and run a bi-directional test.


Two other things spring to mind though;


1)     Will an 1841 handle 50mbit? check the routerperformance PDF.


2)     I recall seeing in a tech note somewhere before that the bandwith on a tunnel interface is limited to 8 or maybe 10mbit depending on the feature set of the IOS. I can't find that note now, but I'm sure a search might get it.


HTH


Kevin


EDIT: Although, as Edison notes, If you get those speeds between the same two hosts with concurrent sessions then it is likely to be a host problem.


Message was edited by: Kevin Brennan

Leo Laohoo Wed, 07/28/2010 - 16:18
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I recall seeing in a tech note somewhere before that the bandwith on a tunnel interface is limited to 8 or maybe 10mbit depending on the feature set of the IOS.

You're very correct there.  Default is at 8Mbps and if one is to use the Advanced IP feature set you can change the value.

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