[Bug 203630] [Hyper-V] [nat] [tcp] 10.2 NAT bug in TCP stack or hyperv netsvc driver

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=203630

--- Comment #5 from onyx at netfusion.fr ---
I encounter the same problem in a slightly different configuration:

- Hyper-V 2012, hosting:
-- FreeBSD 10.2 x64 with MPD acting as a PPTP server
-- Windows 7
- Clients on the LAN (misc OS), inclding an old FreeBSD 6.1
- Clients connected to FreeBSD 10.2 VM by PPTP (MPD5) using misc OS as well

Firewalls turned off.

* TCP, UDP, ICMP work:
 - between all PPTP clients
 - between a PPTP client, FreeBSD and the Windows 7 virtual machine
 - between FreeBSD and local machines on the LAN

* TCP doesn't work between a PPTP client and machines on the LAN.

I tried to investigate by opening a TCP connection on port 80 from a PPTP
client to the old FreeBSD 6.1 on the LAN. There is a part of the tcpdump I ran
on that old FreeBSD 6.1:

IP (tos 0x0, ttl 127, id 20111, offset 0, flags [DF], proto: TCP (6), length:
48) pc-ed.lan.domain.fr.56026 > srv-mandy.lan.domain.fr.http: S, cksum 0x84d6
(incorrect (-> 0x7c54), 2429810306:2429810306(0) win 8192 <mss
1354,nop,nop,sackOK>

I have read that having an incorrect checksum was normal, so I guess the
problem doesn't come from that.

>From what I saw, the problem occurs as long as the FreeBSD 10.2 is used as a
gateway (NAT or not).

Let me know if I can do other tests to help you investigate the problem. Any
help would be appreciated.

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