From owner-freebsd-virtualization@freebsd.org Wed Dec 21 16:08:39 2016 Return-Path: Delivered-To: freebsd-virtualization@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A90D3C8A0DC for ; Wed, 21 Dec 2016 16:08:39 +0000 (UTC) (envelope-from freebsd@omnilan.de) Received: from mx0.gentlemail.de (mx0.gentlemail.de [IPv6:2a00:e10:2800::a130]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 30C151C30 for ; Wed, 21 Dec 2016 16:08:39 +0000 (UTC) (envelope-from freebsd@omnilan.de) Received: from mh0.gentlemail.de (ezra.dcm1.omnilan.net [78.138.80.135]) by mx0.gentlemail.de (8.14.5/8.14.5) with ESMTP id uBLG8ZFK041806 for ; Wed, 21 Dec 2016 17:08:35 +0100 (CET) (envelope-from freebsd@omnilan.de) Received: from titan.inop.mo1.omnilan.net (titan.inop.mo1.omnilan.net [IPv6:2001:a60:f0bb:1::3:1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by mh0.gentlemail.de (Postfix) with ESMTPSA id 6A5193ED; Wed, 21 Dec 2016 17:08:35 +0100 (CET) Message-ID: <585AA902.50907@omnilan.de> Date: Wed, 21 Dec 2016 17:08:34 +0100 From: Harry Schmalzbauer Organization: OmniLAN User-Agent: Mozilla/5.0 (X11; U; FreeBSD i386; de-DE; rv:1.9.2.8) Gecko/20100906 Lightning/1.0b2 Thunderbird/3.1.2 MIME-Version: 1.0 To: freebsd-virtualization@freebsd.org Subject: Jumbo frames truncated at 4084 bytes by virtio-net? (using if_bridge(4) and vtnet(4) with mtu 9000) Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit X-Greylist: ACL 119 matched, not delayed by milter-greylist-4.2.7 (mx0.gentlemail.de [78.138.80.130]); Wed, 21 Dec 2016 17:08:35 +0100 (CET) X-Milter: Spamilter (Reciever: mx0.gentlemail.de; Sender-ip: 78.138.80.135; Sender-helo: mh0.gentlemail.de; ) X-BeenThere: freebsd-virtualization@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Discussion of various virtualization techniques FreeBSD supports." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 21 Dec 2016 16:08:39 -0000 Hello, I'm having guest connectivity problems with jumbo frames. Since if_bridge(4) requires all interfaces to have the same MTU (and the uplink interface also handles iscsi traffic, which greatly benefits from jumbo frames), I 'ifconfig create vmnet0 mtu 9000' Afert adding it to the bridge 'ifconfig bregn addm vmnet0' and setting guest mtu to 9000 (which vtnet(4) claims to support), I can transceive frames larger than 1500, which this flow from the guest's vtnet(4) interface demonstrates: 16:54:36.672709 00:a0:98:73:9f:42 > 96:07:e9:78:c6:ac, ethertype IPv4 (0x0800), length 4084: 172.21.35.1 > 172.21.35.32: ICMP echo request, id 56840, seq 0, length 4050 16:54:36.672791 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4 (0x0800), length 4084: 172.21.35.32 > 172.21.35.1: ICMP echo reply, id 56840, seq 0, length 4050 On the host this looks similar. Now with a payload size of 4043 instead of 4042 bytes, the reply never makes it through virtio-net: Host flow: 16:57:06.641382 00:a0:98:73:9f:42 > 96:07:e9:78:c6:ac, ethertype IPv4 (0x0800), length 4085: 172.21.35.1 > 172.21.35.32: ICMP echo request, id 27401, seq 0, length 4051 16:57:06.641399 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4 (0x0800), length 4085: 172.21.35.32 > 172.21.35.1: ICMP echo reply, id 27401, seq 0, length 4051 Guest flow: 16:57:06.642073 00:a0:98:73:9f:42 > 96:07:e9:78:c6:ac, ethertype IPv4 (0x0800), length 4085: 172.21.35.1 > 172.21.35.32: ICMP echo request, id 27401, seq 0, length 4051 16:57:06.642233 96:07:e9:78:c6:ac > 00:a0:98:73:9f:42, ethertype IPv4 (0x0800), length 4084: truncated-ip - 1 bytes missing! 172.21.35.32 > 172.21.35.1: ICMP echo reply, id 27401, seq 0, length 405 Now my problem is that I can't simply keep guest's mtu at 1500, since the host will send jumbo frames as answer wich never get through virtio-net. Does anybody have an idea how to fix/work arround? Thanks, -harry