UDP traffic, msg size exceeds 9215 Bytes

Steven Hartland killing at multiplay.co.uk
Thu Nov 28 16:02:14 UTC 2013

You really shouldnt allow the application to send packets that big
as you'll end up with fragmentation and due to UDP protocol issues
and hackers abusing them (the port for fragemented packets isn't set)
you'll often find fragmented udp packets are simply blocked.


----- Original Message ----- 
From: "Marc Olzheim" <marcolz at stack.nl>
To: "Meny Yossefi" <menyy at mellanox.com>
Cc: <freebsd-net at freebsd.org>; "Oded Shanoon" <odeds at mellanox.com>
Sent: Thursday, November 28, 2013 12:49 PM
Subject: Re: UDP traffic, msg size exceeds 9215 Bytes

> On Thu, Nov 28, 2013 at 12:43:43PM +0000, Meny Yossefi wrote:
>> Hi all,
>> We've been running some benchmarks (Netperf, Iperf) on our driver (Mellanox), and witnessed an odd behavior.
>> We saw that when running UDP traffic with msg size larger than 9215 bytes, it gets dropped for some reason. MTU is 1500.
>> We've spotted the same behavior on different vendors which lead us to believe there's some kernel issue that we are missing 
>> here.
> Did you meddle with sysctl net.inet.udp.maxdgram yet ? The default value is
> 6 * 1536 = 9216 bytes...
> Marc
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