Date: Wed, 21 Dec 2016 17:40:28 +0100 From: Harry Schmalzbauer <freebsd@omnilan.de> To: freebsd-virtualization@freebsd.org Subject: Re: Jumbo frames truncated at 4084 bytes by virtio-net? (using if_bridge(4) and vtnet(4) with mtu 9000) Message-ID: <585AB07C.6010604@omnilan.de> In-Reply-To: <585AA902.50907@omnilan.de> References: <585AA902.50907@omnilan.de>
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Bezüglich Harry Schmalzbauer's Nachricht vom 21.12.2016 17:08 (localtime): … > 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? For the records, replacing virtio-net with e1000 (as bhyve PCI-slot-resident) solves the jumbo frame issue! It seems 82545EM is fully emulated (not 82545GM which doesn't support jumbo frames) :-) Thank you very much for this nice work! mav's commit (r302504) mentions heavy performance penalties (factor 2). Has anyone tried the influence of disabling/keeping offload functions in the guest? Thanks, -Harry
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