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 id 1ZCV7K-000DM1-PE; Tue, 07 Jul 2015 18:49:06 +0300
Date: Tue, 7 Jul 2015 18:49:06 +0300
From: Slawa Olhovchenkov <slw@zxy.spb.ru>
To: Pavel Timofeev <timp87@gmail.com>
Cc: freebsd-current@freebsd.org,
 "freebsd-virtualization@freebsd.org" <freebsd-virtualization@freebsd.org>
Subject: Re: MS DNS doesn't answer to CURRENT under Hyper-V
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On Tue, Jul 07, 2015 at 06:04:46PM +0300, Pavel Timofeev wrote:

> Well, turning off checksum offloading by `ifconfig hn0 -txcsum
> -rxcsum` definitely helps.
> 
> As for tcpdump I'm not completely sure if I did it right, but I see
> "bad udp cksum" phrase:
> 
> # tcpdump -i hn0 -vvv -nn udp dst port 53
> tcpdump: listening on hn0, link-type EN10MB (Ethernet), capture size
> 262144 bytes
> 18:01:19.139994 IP (tos 0x0, ttl 64, id 61218, offset 0, flags [none],
> proto UDP (17), length 51)
>     192.168.25.26.45683 > 192.168.25.3.53: [bad udp cksum 0xb39e ->
> 0xf210!] 52886+ A? ya.ru. (23)
> 18:01:24.140544 IP (tos 0x0, ttl 64, id 17293, offset 0, flags [none],
> proto UDP (17), length 51)
>     192.168.25.26.12575 > 192.168.25.3.53: [bad udp cksum 0xb39e ->
> 0x7365!] 52886+ A? ya.ru. (23)

tcpdump "bad udp cksum" is normal on FreeBSD host in case checksum
offload (and may be need only for help finding issuse in code). Need
wireshark capturing from MS DNS host (or from mirroring port).