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Date:      Sat, 08 Mar 2025 15:35:10 -0500
From:      "Dan Langille" <dan@langille.org>
To:        "Marek Zarychta" <zarychtam@plan-b.pwste.edu.pl>, net@freebsd.org
Subject:   Re: Errors over VPN - message authentication code incorrect
Message-ID:  <d4b473c1-f270-49a0-ba8e-adf617639a52@app.fastmail.com>
In-Reply-To: <0496b019-56c9-49f7-bd81-ad5a673bdcfa@app.fastmail.com>
References:  <78e829b4-3f53-4b63-ba0a-fe41b5a36203@app.fastmail.com> <9ea41f25-5a89-47e3-8df2-f973d6f9e41d@plan-b.pwste.edu.pl> <0496b019-56c9-49f7-bd81-ad5a673bdcfa@app.fastmail.com>

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On Sat, Mar 8, 2025, at 1:02 PM, Dan Langille wrote:
> On Sat, Mar 8, 2025, at 11:15 AM, Marek Zarychta wrote:
>> W dniu 8.03.2025 o 13:07, Dan Langille pisze:
>>> Hello,
>>>
>>> I am getting errors when transferring data over my VPN.  I'm not sure why. I've recently replace the gateway / firewall device. Previously, this VPN was stable and these types of transfers worked without error.
>>>
>>> Here is an example.  mydev is behind the firewall. r720-02 is accessed over the VPN
>>>
>>> [12:04 mydev dvl ~/tmp] % time scp -r dvl@r720-02.vpn.unixathome.org:bacula.dump .
>>> bacula.dump              0%    0     0.0KB/s   --:-- ETAFssh_ssh_dispatch_run_fatal: Connection to 10.10.0.217 port 22: message authentication code incorrect
>>> scp: Connection closed
>>> scp -r dvl@r720-02:bacula.dump .  0.14s user 0.01s system 21% cpu 0.665 total
>>>
>>> If I try the scp direct, without using the VPN, the copy succeeds.
>>>
>>> Ideas please?
>>
>> Hello Dan,
>>
>> I'm not sure what type of VPN it is, but if it's OpenVPN, you might need 
>> to add "tun-mtu 1400" on the server side. Please refer to PR 276838.
>
> Yes, this is OpenVPN 2.6.13 on FreeBSD 14.2
>
> I just tried "tun-mtu 1400" on the server side. I restarted all 
> clients.  Problem persists.
>
> I also added "mssfix" to the server, restarted server, restarted all 
> clients. Problem persists. As I read the PR again, it mentions "As of 
> today, kernel openvpn does not seem to support `mssfix` - I'm not sure 
> what "kernel openvpn" is.
>
> The server configuration contains 'disable-dco'.
>
> PR 276838 mentions DCO, so given it is disabled, wtf?
>
> I notice that the problem exists on all the OpenVPN client except one. 
> That client is on FreeBSD 14.2, the failing clients are all on FreeBSD 
> 14.1 - hmmm. That is curious.  Perhaps I should update one of the 
> clients and try again.

I updated one host (tallboy) from FreeBSD 14.1 to FreeBSD 14.2 - initial tests
are good. Not seeing the problem on an scp which previously failed. Now doing 
the real test: Bacula backup over OpenVPN - about 8-9GB.

I should know more by about 2145 UTC today - that's about how long that backup
should take, based on the February full backup.
-- 
  Dan Langille
  dan@langille.org



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