From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ABD9EC433E0 for ; Wed, 27 May 2020 21:39:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E3E42075A for ; Wed, 27 May 2020 21:39:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726482AbgE0Vjn (ORCPT ); Wed, 27 May 2020 17:39:43 -0400 Received: from correo.us.es ([193.147.175.20]:40426 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726114AbgE0Vjm (ORCPT ); Wed, 27 May 2020 17:39:42 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 216CF9F4C5 for ; Wed, 27 May 2020 23:39:40 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 12D16DA710 for ; Wed, 27 May 2020 23:39:40 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id 08224DA703; Wed, 27 May 2020 23:39:40 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 227D2DA703; Wed, 27 May 2020 23:39:38 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Wed, 27 May 2020 23:39:38 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (unknown [90.77.255.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id 05D3B42EF4E0; Wed, 27 May 2020 23:39:37 +0200 (CEST) Date: Wed, 27 May 2020 23:39:37 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Michael Braun Cc: netfilter-devel@vger.kernel.org Subject: Re: [PATCH 0/3] Avoid gretap fragmentation with nftables on bridge Message-ID: <20200527213937.GA2714@salvia> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-Virus-Scanned: ClamAV using ClamSMTP Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Wed, May 06, 2020 at 11:46:22AM +0200, Michael Braun wrote: > Hi, > > I have a bridge with connects an gretap tunnel with some ethernet lan. > On the gretap device I use ignore-df to avoid packets being lost without > icmp reject to the sender of the bridged packet. > > Still I want to avoid packet fragmentation with the gretap packets. > So I though about adding an nftables rule like this: > > nft insert rule bridge filter FORWARD \ > ip protocol tcp \ > ip length > 1400 \ > ip frag-off & 0x4000 != 0 \ > reject with icmp type frag-needed > > This would reject all tcp packets with ip dont-fragment bit set that are > bigger than some threshold (here 1400 bytes). The sender would then receive > ICMP unreachable - fragmentation needed and reduce its packet size (as > defined with PMTU). Patches 1 and 2 are applied, thanks. Patch 3 has been merged upstream as a bugfix since VLAN should be preversed in any reject case.