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 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 (eyal(a)eyal.emu.id.au)
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