On 12/11/2023 10.06, fedora(a)eyal.emu.id.au wrote:
On 12/11/23 09:16, Roger Heflin wrote:
> If connections/files/stuff passes that is less than 1 network packet
> (about 1500 bytes - header--say 1460 give or take) then this is a sign
> that a piece of the network somehow has the wrong MTU size.
>
> I have seen network ports not get their MTU set to 1502 or 1504 and
> when this happens it causes the MTU on the network to be 2-4 bytes
> short and causes havoc.
>
> Routers have done similar things. I have seen network port restarts
> sometimes cause the MTU to be wrong.
>
> ping -s 1400 <target> and ping -s 2000 <target> if 2000 fails then
> raise the 1400 by 2 bytes at a time until it starts failing (or do a
> binary search for it, but it is going to be under 1500).
>
> Lower your main host interface's MTU by say 4 and retest, if that
> "fixes" it that is a sign that this is the issue.
It did fix it. I initially dropped the MTU to 1400 and now all uploads work.
I hope email will go out now too. I will fine tune it later.
I now verified that it all works with MTU down (from 1500) to 1456 (using ifconfig), but
fails with 1458 or above.
Until the problem is resolved by my ISP I updated
/etc/sysconfig/network-scripts/ifcfg-eth1
eyal
I have an open case with my ISP who are in charge of my modem etc.
and I think they
are involved in the problem.
Thanks everyone
Eyal
> On Sat, Nov 11, 2023 at 4:08 PM <fedora(a)eyal.emu.id.au> wrote:
>>
>> Since the middle of the night on 7/Nov, uploading files with ssh is problematic.
>>
>> My SMTP server requires SSL/TLS security, and uploading files to the same site
requires sftp.
>> So both run over ssh.
>>
>> I have a few scripts that run from cron and send me mail when required.
>> They also upload some files for other people and for me when I am away from
home.
>>
>> Now here is the problem. Small files pass though just fine. Using sftp I
measured
>> that files up to 1300 bytes upload, but anything larger hangs. Large mail is also
blocked,
>> queued as seen in mailq:
>> (timeout writing message to xxxx.xxxx.net.au.: Connection timed)
>>
>> It seems that after some time (often hours) things resolve.
>> Rebooting the machine also allows the mail through.
>>
>> Scripts that upload larger files (using lftp) hang for hours.
>>
>> Now I tested the same from a laptop over 4G and it does not show any of these
problems.
>> So it is probably not at the receiving end (I also asked them).
>> All they see is occasional timeouts on mail and ssh (from me).
>>
>> I cannot figure what can do this. Small files upload OK larger ones hang???
>>
>> I said earlier "middle of the night" because I was not at my computer
then and
>> nothing of note that I could see, but the problems started showing in the logs.
>>
>> There is still the possibility of my ISP fiddling with the modem remotely (in
the
>> past they did it around this time). I am chasing them.
>>
>> One thing that can help now is a way to un-hang the uploads without having to
reboot.
>> I do not know where to even look.
>>
>> Some details:
>>
>> The modem uses 4G for wireless internet.
>>
>> I used a laptop wired to my server, then wired to the modem, then connected to my
WiFi ap
>> (which is wired to the modem) and all hang on large(ish) uploads.
>>
>> Only when I connected the laptop to my phone (as a WiFi ap) things worked well.
>>
>> BTW, one thing I did was disable ipv6 but the problem persists.
>>
>> --
>> Eyal at Home (fedora(a)eyal.emu.id.au)
--
Eyal at Home (fedora(a)eyal.emu.id.au)