[c-nsp] Performance issue on link

[Laurent Geyer]

You didn't adjust the TCP window size of the stack. 


Wish I could remember the exact syntax, but if you do a google search you should find the systl commands to make the necessary changes for the protocol stack.
—
Laurent

On Mon, Apr 1, 2013 at 7:08 PM, CiscoNSP List <cisconsp_list at hotmail.com>
wrote:

> Thanks for the reply - I am testing from two Linux servers, and as mentioned, I adjusted the tcp window size in IPERF (-w), but it actually made the performance worse?
> Date: Mon, 1 Apr 2013 16:04:37 -0700
> From: geyer.laurent at gmail.com
> To: cisconsp_list at hotmail.com
> CC: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] Performance issue on link
> Bandwidth delay product (BDP).
> You'll find a bunch of articles out there searching for those terms. Adjusting the TCP windows size to compensate for the delay should help you achieve close to CIR.
> You mention a Linux server (most distributions have TCP window scaling enabled), but I'll venture to say you're testing from a Windows client.
> Windows systems are notoriously poor at dealing with BDP without some fine tuning.
> BDP would certainly explain the discrepancy between UDP and TCP throughput.—
> Laurent
> On Mon, Apr 1, 2013 at 6:56 PM, CiscoNSP List <cisconsp_list at hotmail.com> wrote:
> Hi,
> We have a 40Mb link between 2 POPs - Latency ~65m/sec (No packet-loss)
> POP A Is a 7301 and 2960POP B is a 7200 and 4948
> 40Mb link is connected to the two switches (L2), and then a trunk link to both routers for all L3.
> Have a Linux server connected to both switches, and achieve the following performance:
> IPERF (UDP)
> POP A -> POP B - 38.5Mb/secPOP B -> POP A - 38.5Mb/sec
> IPERF (TCP)
> POP A -> POP B - ~20Mb/secPOP B -> POP A - ~12Mb/sec
> FTP
> POP A -> POP B - ~38Mb/secPOP B -> POP A - ~16Mb/sec
> WGET
> POP A -> POP B - ~30Mb/sec POP B -> POP A - ~16Mb/sec
> Any suggestions on why I am seeing poor performance with TCP transfers? (Especially POP B -> POP A direction) - I've tried adjusting the window size in IPERF but it actually made the results worse?
> Thanks in advance.
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