From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: More details on why received UDP packets are treated as errors? Date: Mon, 29 Jul 2013 13:21:32 -0700 Message-ID: <1375129292.10515.21.camel@edumazet-glaptop> References: <51F6B2AB.5050607@candelatech.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev To: Ben Greear Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:37295 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754491Ab3G2UVe (ORCPT ); Mon, 29 Jul 2013 16:21:34 -0400 Received: by mail-pb0-f46.google.com with SMTP id rq2so1361744pbb.5 for ; Mon, 29 Jul 2013 13:21:33 -0700 (PDT) In-Reply-To: <51F6B2AB.5050607@candelatech.com> Sender: netdev-owner@vger.kernel.org List-ID: 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/