From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arif Hossain Subject: How to get notified if packets are dropped because of checksum mismatch error Date: Fri, 16 Mar 2012 18:18:00 +0600 Message-ID: <1331900280.4147.15.camel@arifLaptop> Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha1"; protocol="application/pgp-signature"; boundary="=-ANOmd0vkFsJ0qtCTRVoQ" To: netfilter , netfilter-devel Return-path: Received: from mail-gx0-f174.google.com ([209.85.161.174]:47768 "EHLO mail-gx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761740Ab2CPMSL (ORCPT ); Fri, 16 Mar 2012 08:18:11 -0400 Sender: netfilter-devel-owner@vger.kernel.org List-ID: --=-ANOmd0vkFsJ0qtCTRVoQ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi all, I have a netfilter_queue app which de-obfuscates a already obfuscated udp packets. de-obfuscation process ends successfully but somehow packet is not reaching to the udp daemon. i'm suspecting this is happening because of a udp checksum mismatch. so i'm wondering how can i get logs of packets which are dropped because of udp checksum mismatch? I'm receiving the packets ok in my netfilter_queue app. and when i issue set_nfq_verdict() it also returns a positive value. problem is packet is not delivered to the udp daemon i'm expecting. i've straced my netfilter_queue app. it shows that it issues a sendmsg() to the udp socket which is listening for this. I've also straced my udp daemon. its stuck in poll() for receiving udp packet. but it does not return from this poll meaning that something is wrong. packet is lost in oblivion after set_nfq_verdict(). how can i debug it? i've heard linux by default dropps a packet if it does not have correct checksum if checksum is present, this behavior can be modified by recompiling the kernel. using a custom kernel is not in our agenda. my platform : Linux 2.6.32-220.7.1.el6.x86_64 #1 SMP Wed Mar 7 00:52:02 GMT 2012 x86_64 x86_64 x86_64 GNU/Linux --=-ANOmd0vkFsJ0qtCTRVoQ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) iQEcBAABAgAGBQJPYy94AAoJEDcRh2vIjPwjVrsH/0NETQjmR4XwyCzClhgCGG4y PKrnkfrI1+/5PtklqeUet3IbMKw6iza/Eiqixk0b87NnIyffoazGk6dIHaPgFNUU uIU3uAgflSX49gBStSW+R9oJfzWRK/qQKJ4bSmR0W6aYoMHGGK1+fHhBrghvAQxP iNFVXgDMvFKEPGnAAjDp2lNSJoV18RXdyj5iOY7YuuTaGIeWOi6B6HOOVw3ctBF5 Yz0Bel159mpT/QKXBRaLFNBa84jx2S8M04MYLgtI3vb8Zu06gZ/+WQjjMDO6zGwa WWPBBktWdKXn2zyWkVS5shB5VcdwyOeRbglUsDx8JuoKrgezM6Z22lKadtahrSg= =8FCv -----END PGP SIGNATURE----- --=-ANOmd0vkFsJ0qtCTRVoQ--