bug#71238: Installer image consistently fails to run system init due to TLS error

[Roman Riabenko]

Hello

I had a similar issue with a 6to4 tunnel but I guess that the same
cause may be relevant to a VPN or some other type of connection that
affects the MTU.

The pull operation would fail sporadically, usually on the same package
— most of the time that would be a relatively large package like the
kernel but not necessarily. The failure would often be a TLS failure
but I found it to be a common failure when there is a connectivity
issue because it is the TLS that tries to establish or restore the
connection.

I admit that I had similar issues with connecting to just a few
seemingly random websites over the tunnel, but the download of
substitutes from the bordeaux server seemed to be the most affected.
The tunnel customer support suggested that it is an MTU issue. I tried
a lot of different MTU values. Some of the values I tried fixed all my
connection issues except for the pull operation until I found how to
set up the tunnel in a way that automatically discovers and changes the
MTU dynamically.

I thought it was too specific to my router, so I posted my findings
elsewhere: "How can I set up 6to4 on MikroTik and configure MTU to fix
connection failures and update guix?"
https://superuser.com/q/1808662/1203531

I recently followed a link to this bug report from a help mailing list
thread:
"guix pull/guix upgrade often fails over VPN with TLS error message"
https://lists.gnu.org/archive/html/help-guix/2024-09/msg00014.html
I found the descriptions of the issue familiar, so I am sharing an idea
that it might be related to the MTU of the connection to the substitute
server.

Roman

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