From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi1-f170.google.com (mail-oi1-f170.google.com [209.85.167.170]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 600041BED74 for ; Tue, 30 Apr 2024 22:22:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.167.170 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714515725; cv=none; b=uTlR9Eod2vzuaFO7QjziNvq8lreCbFuQY0FaAdR8J75HBhStAZAIdcFTN6InjvFQhOejdMUR1M4p2q6GDXxdwveyY4FjaNq8dM65/Dp3ORfK1g1UoRBCnJYp6zFoVpICHQB2mmwNmfQ5XBlrzfoxacQ62F/ThFTkMoTn2BbBbgQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714515725; c=relaxed/simple; bh=oLnatKC911WlLd6QdiNrEPIYBzicSikdY8AzFjduVEA=; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; b=R+ryx/sewXG7WrNrUoGi2sGWeKDtPvxLnMvWAZVW+8EKdgeJ3p2FV5UCZj8hI9ecxdJmjve/uidftgZm1W+TWgUJh9bQlILKo+O0svKqzqBeJJZDHvCODBjK5xhkPCNOSKwmTQmorPBj8V6SR1OX8vfNi9P+enice7Oh5lV4z9U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=RMOkLs8l; arc=none smtp.client-ip=209.85.167.170 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="RMOkLs8l" Received: by mail-oi1-f170.google.com with SMTP id 5614622812f47-3c868e82bf8so1123319b6e.0 for ; Tue, 30 Apr 2024 15:22:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1714515723; x=1715120523; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:subject:to:from :date:from:to:cc:subject:date:message-id:reply-to; bh=9Qo40fDJ/kAHcAkZNJ8QaQrQsN30A87gDIVLpqzHoHk=; b=RMOkLs8l3bhVFPrYN75voVs7rCoYIlgEMTut5k7PoXFOqVvJ8o2WOCOD/+f3zeCRSH ASOY8MgNlsXt61YBU9NC54nAFx/wJes53K1d4WgRjB8Ijqj6DrSpQ08pPcJDzAB4laVx o+Lk95lohuQxSd9YYJU4DHNQwtZ54vSgqfIthVXvtBL/GrEWNXxqNC9g2VSEloMdL53v QfppEDe3Rn8MbGlPZn+O5dxlVH6ZMIBHj9BW769uPWEATkWeOYv8IWtXc3FxEUNV5ry8 bYlZwSWG7ZyYUmUoiZ+1WkHfbJZot/uaDgxXrF+1yvlpDUzfA6J9VtEJDJgX/4STXuor DAJA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1714515723; x=1715120523; h=content-transfer-encoding:mime-version:message-id:subject:to:from :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=9Qo40fDJ/kAHcAkZNJ8QaQrQsN30A87gDIVLpqzHoHk=; b=lkzgPXWTPVBYn9zfndQk+BtwghrfsdlvaiVCBchKG7j8AkmCEm/YHYIAbYCGlcKtqn GCIiCAXFWiiB3ZfVPLfY6hoxxunqIkJEsOS/Z+DiwLoKpWOAW0e4LQAU+Ep7AHXeTIiD m3ypuW2rkbl7UMUxgDz0IBhsCyP8qbs243CsLfPusbs5H3lnMMH7sUEuruKG0M5SjLPJ 9lP2SyfAnsCgXvrcvPa6u3eleeCiVdCM2l3Auzb0SSygqKg9XpVgbTZWRyWALHNUexT+ vwn31YaKuGNdnQUWM7IkSuGjqXccQ82TtE/sggXNRGDQP3PHdJ0k6iRBtS469fxy2rlT SuEQ== X-Gm-Message-State: AOJu0YyVXkRV/iPfNswYjRX62o2DusGRY61rnROIuok+1WEh1+0hJVHK V4KWl99ESoS2MFHfpJFZQNX53+/BxKcRHuB5EubaV2SPRGdueeDvPJTXEA5G X-Google-Smtp-Source: AGHT+IEkpWUHKGPtdtcRMBu3gy8fs9neR+fVeYlsv13j4y5O4X77SiwIvCja5CzYiHiVzYWuqw9T3A== X-Received: by 2002:a05:6808:4c1:b0:3c5:fed9:ea36 with SMTP id a1-20020a05680804c100b003c5fed9ea36mr1009953oie.3.1714515723349; Tue, 30 Apr 2024 15:22:03 -0700 (PDT) Received: from playground ([204.111.226.63]) by smtp.gmail.com with ESMTPSA id s2-20020ae9f702000000b0078efd872d3csm11833546qkg.14.2024.04.30.15.22.03 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 30 Apr 2024 15:22:03 -0700 (PDT) Date: Tue, 30 Apr 2024 18:22:00 -0400 From: To: netfilter@vger.kernel.org Subject: IPv4 NAT and lo, and iptables Message-ID: <20240430182200.39ac9ea1@playground> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: netfilter@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit I just encountered a linux/netfilter oddity. Simplified, I have FW_A with iface PUB to internet, another to internal LAN_1 and a third to LAN_2. Firewall rules on FW_A are properly set to: - NAT traffic to/from PUB, - block LAN_2 traffic from LAN_1 - allow LAN_1 traffic to LAN_2 - forward internet traffic to port 80 to SRVA_2 on LAN_2 On FW_A, in mangle:PREROUTING, XMARKs are set for traffic coming from LAN_1 and LAN_2. Example: iptables -A portfwb -d 192.0.2.77/32 -i LAN_1 \ -j MARK --set-xmark 0x1/0xffffffff Internet hosts access port 80 on SRVA_2. Hosts on LAN_1 access port 80 on SRVA_2 via the public IP. Even SRVA_2 can access itself (port 80) via the public IP. What *doesn't* work is FW_A accessing port 80 on SRVA_2. This traffic does not get NATted and appears on lo with the public address(es). And since nothing on FW_A listens to port 80, the connection is rejected. I *expected* locally-generate traffic to be NATted just like remote traffic. Questions: - Is lo ignored in PREROUTING? - Is it possible to DNAT local traffic on FW_A (changing) the public IP to the private IP on LAN_2? - Would I specify '-i lo' in mangle:PREROUTING and nat:PREROUTING (as I do for the real NICs)? The uber questions are: - Should I be able to DNAT and SNAT traffic on lo just as I can on other LANs, or do I need to take extra steps? - Is this a known oddity? or was it known back around Linux 3.16 and iptables 1.6? (Don't ask; sometimes we're stuck in a place we don't want to be.) Thanks, Neal