From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gao feng Subject: Re: nat drop the icmp redirect packet Date: Thu, 01 Dec 2011 08:59:56 +0800 Message-ID: <4ED6D18C.7000802@cn.fujitsu.com> References: <4ED2E00B.3000006@cn.fujitsu.com> <4ED67BB1.8020808@trash.net> Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netfilter-devel@vger.kernel.org, pablo@netfilter.org To: Patrick McHardy Return-path: Received: from cn.fujitsu.com ([222.73.24.84]:64563 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753476Ab1LAA7O convert rfc822-to-8bit (ORCPT ); Wed, 30 Nov 2011 19:59:14 -0500 In-Reply-To: <4ED67BB1.8020808@trash.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: =D3=DA 2011=C4=EA12=D4=C201=C8=D5 02:53, Patrick McHardy =D0=B4=B5=C0: > On 11/28/2011 02:12 AM, Gao feng wrote: >> Hi >> >> In func nf_nat_icmp_reply_translation,the icmp packet will be droped= when the nat is not finished. >> pc A(whose gateway is C) send a icmp request to pc B. >> When gw C receive this packet,it may return a icmp redirect packet t= o A. >> BUT now,the icmp request packet has not go to POSTROUTING,So the nat= is not finished. >> Finally,the icmp redirect packet will be droped no matter the conn h= as nat or not. >> >> of course,the icmp redirect packet will be correct handled when nat = is finished. >> >> Can somebody will give me some suggestion, >> or should I just add a sysctl to let the user decide drop or receive= this icmp redirect packet when nat is not finished? >=20 > It doesn't matter whether the ICMP packet has gone through > POST_ROUTING, the conntrack associated with the packet is > that of the original packet causing the ICMP REDIRECT (or > any other kind of ICMP error). >=20 > Basically, we don't want hosts talking directly to each other > *if* NAT has been set up since that would obviously break > things. In the case you describe (only destination NAT setup > completed, but null mapping) instead of dropping the packet, > we could set up a null source mapping and let the packet > through under the assumption that the hosts will then start > communicating directly. >=20 > This will break if the host receiving the ICMP REDIRECT ignores > it though. What is the specific problem you're trying to solve? >=20 Thanks Patrick! As I said,in my case,the *first* ICMP REDIRECT packet will be dropped e= ven the system has no nat rules,because this REDIRECT packet is triggered by the original packet in FORWARD chain(ip_forward),and when this REDIR= ECT packet goto POSTROUTING chian(nf_nat_fn->nf_nat_icmp_reply_translation)= ,the original packet is still in FORWARD chain.So the original packet's conn= track ONLY has IPS_DST_NAT_DONE. I understand your mean,we should not let REDIRECT to take effect when t= his conntrack has nat rule. I just want to know is there some idea to avoid the first ICMP_REDIRECT= packet being dropped? -- To unsubscribe from this list: send the line "unsubscribe netfilter-dev= el" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html