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Openssl

Lasse Thorbro-Steenberg
Hi,

New to this list!

I am using Openssl in a project that send large amounts of data in bursts from a windows 2008 server to an Ubuntu 16.04 client.
It works well with low data rates (<1mbs) but when mean data rates hits around 2 mbs, things get ugly. I use blocking wrtite calls and my buffers overflow after a while at 2mbs.
Using Wireshark I can see the TCP window remains open, but after a few seconds on 2mbs the server start fragmenting IP packets which completely drops the throughput to around 1 mbs.
Data is delivered successfully even with fragmentation, but the effective throughput achievable on the link drops significantly.

Has anyone seen this type of issue before ?

Thanks,
Lasse

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Re: Network problems (not OpenSSL)

Viktor Dukhovni

> On Apr 19, 2017, at 10:39 AM, Lasse Thorbro-Steenberg <[hidden email]> wrote:
>
> Using Wireshark I can see the TCP window remains open, but after a few seconds on 2mbs the server start fragmenting IP packets which completely drops the throughput to around 1 mbs.
> Data is delivered successfully even with fragmentation, but the effective throughput achievable on the link drops significantly.

OpenSSL does not implement TCP/IP, and network throughput issues
need to solved at the network layer.  You may have path MTU issues,
or other networking problems.  If smaller than the MTU writes are
done back to back, you may want to disable Nagle's algorithm via
the appropriate setsockopt() call (enable TCP_NDELAY).

You should be able to see the same throughput issues just sending
data (similarly chunked) in the clear without OpenSSL.

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        Viktor.
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