-----Original Message-----
From: Padam Jeet Singh <padam.si...@inventum.net>
Date: Sunday, June 17, 2018 at 12:00 PM
To: Stephen Hemminger <step...@networkplumber.org>
Cc: "dev@dpdk.org" <dev@dpdk.org>, Yong Wang <yongw...@vmware.com>
Subject: Re: [dpdk-dev] vmxnet3 TX TCP/UDP checksum not getting computed with
L2_len > 14
>> On 17-Jun-2018, at 10:16 PM, Stephen Hemminger
<step...@networkplumber.org> wrote:
>>
>> On Sun, 17 Jun 2018 14:55:06 +0530
>> Padam Jeet Singh <padam.si...@inventum.net> wrote:
>>
>>> Hello,
>>>
>>> Issue observed when using vmxnet3 based interface on packet with
following structure is sent:
>>>
>>> Ethernet + PPPoE + PPP (22 bytes) as the Layer 2 header,
>>> IPv4 (20)
>>> UDP
>>> DNS Payload
>>>
>>> The tx offload value in this case is 0x0f0000000000000 (PKT_TX_IPV4 |
PKT_TX_IP_CKSUM | PKT_TX_UDP_CKSUM)
>>>
>>> The checksum of the packet seen by the receiver shows incorrect
checksum and it’s value is the pseudo checksum value that was set at the time
of the TX. However the IP header checksum is correct.
>>>
>>> The same issue is not seen when the L2 header is a just the Ethernet
(14 bytes).
>>>
>>> Also, with the same setup on the same hardware if we switch the driver
from vmxnet3 to e1000e, all checksums are computed correctly.
>>>
>>> Is this a DPDK vmxnet3 driver bug or that of underlying esxi? The ESXi
version is 6.0.0 (Build 3620759).
>>>
>>> Thanks,
>>> Padam
>>
>> I don't think VMWare supports IP checksum offload. Since IP checksum is
trivial and in cache,
>> the IP header checksum offload is usually not a speed up anyway. Linux
for example, never does
>> IP header checksum offload.
> It’s not the IP checksum - it’s the TCP/UDP checksum (L4) that’s not
getting computed. In fact the IP checksum is coming correctly because we are
handing it in software. The driver when queried returns TX offload flags with
the IP header checksum bit off, but L4 checksum (TCP & UDP) are available. The
UDP checksum gets computed correctly if and only if the l2_len is 14. In case
of other encapsulations, e.g. pppoe (l2_len=22), this checksum computation is
being skipped and the packet is simply sent out with the pseudo checksum value
of the IP header.
Vmxnet3 backend does not support Ethernet + PPPoE + PPP as layer 2 header if l4
checksum if requested.
