netdev - Re: More details on why received UDP packets are treated as errors?

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Message-ID: <1375129292.10515.21.camel@edumazet-glaptop>
Date:	Mon, 29 Jul 2013 13:21:32 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Greear <greearb@...delatech.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: More details on why received UDP packets are treated as errors?

On Mon, 2013-07-29 at 11:21 -0700, Ben Greear wrote:
> We have a test case on 3.9.9+ (local patches applied) where sending from
> VETH interface, through peer VETH bridged (with our own emulator bridge module)
> to physical interface, which is then looped to another physical interface (B).
> The VETH and the wired B interface are sending UDP traffic to each other.
> Routing rules should be configured such that this all works appropriately.
> 
> Replacing our bridging module with a user-space bridge has same behaviour.
> 
> This setup works on the 3.7.y kernel, but we only get one-way traffic
> (B to VETH) on 3.9.9+.
> 
> I sniffed the B port, and traffic appears to be sent and received
> properly (ie, no checksum errors, etc).  But, our user-space app
> shows no received UDP frames on B, and netstat -s gives the
> output below.
> 
> Is there any way to get more details about what these 'packet receive errors'
> are caused by using normal-ish tools?

You could try dropwatch for this kind of obscure drops

https://fedorahosted.org/dropwatch/



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