From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: More details on why received UDP packets are treated as errors? Date: Wed, 07 Aug 2013 17:10:35 -0700 Message-ID: <5202E1FB.8020405@candelatech.com> References: <51F6B2AB.5050607@candelatech.com> <1375129292.10515.21.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev To: Eric Dumazet Return-path: Received: from mail.candelatech.com ([208.74.158.172]:37807 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933310Ab3HHAKg (ORCPT ); Wed, 7 Aug 2013 20:10:36 -0400 In-Reply-To: <1375129292.10515.21.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On 07/29/2013 01:21 PM, Eric Dumazet wrote: > 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/ I had a chance to crank this up today. dropwatch is pretty sweet...turns out it's dropping due to bad UDP checksums, due to the VETH bug/issue where it claims to calculate HW checksum but appearantly does not actually do so (see previous email in another thread). Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com