Bug#1001834: openssh-client: scp 1:8.7p1-2 timeouts when connecting to non LAN machines

Package: openssh-client
Version: 1:8.7p1-2
Severity: normal

Dear Maintainer,
when I use scp on a machine with Debian testing, the command timeouts.
This happens only when connecting to machines on the Internet via my fiber
connection. It does work, instead, when I copy files to other machines in the
LAN, or when I change provider, or when I change scp version.

In fact with a previous scp version, i.e., the one in Debian
stable, 1:8.4p1-5, the problem does not show up.

when I connect to master.debian.org, this is what happens:

$ scp -vvv master.debian.org:key-transition-2014.txt /tmp/
Executing: program /usr/bin/ssh host master.debian.org, user (unspecified), command scp -v -f key-transition-2014.txt
OpenSSH_8.7p1 Debian-2, OpenSSL 1.1.1l  24 Aug 2021
debug1: Reading configuration data /home/myfineuser/.ssh/config
debug1: /home/myfineuser/.ssh/config line 1: Applying options for *
debug1: /home/myfineuser/.ssh/config line 9: Applying options for *.debian.org
debug3: kex names ok: [diffie-hellman-group1-sha1]
[...]
debug3: Ignored env GDMSESSION
debug3: Ignored env DBUS_SESSION_BUS_ADDRESS
debug3: Ignored env _
debug1: Sending command: scp -v -f key-transition-2014.txt
debug2: channel 0: request exec confirm 1
debug3: send packet: type 98
debug2: channel_input_open_confirmation: channel 0: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug3: send packet: type 80
debug3: send packet: type 80
debug3: send packet: type 80
Timeout, server master.debian.org not responding.

when I issue the same command with scp 1:8.4p1-5, the output is (excerpt):

[...]
debug3: Ignored env _
debug1: Sending command: scp -v -f key-transition-2014.txt
debug2: channel 0: request exec confirm 1
debug3: send packet: type 98
debug2: channel_input_open_confirmation: channel 0: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel 0: rcvd adjust 2097152
debug3: receive packet: type 99
debug2: channel_input_status_confirm: type 99 id 0
debug2: exec request accepted on channel 0
debug2: channel 0: rcvd ext data 55
Sending file modes: C0644 3267 key-transition-2014.txt
debug2: channel 0: written 55 to efd 6
Sink: C0644 3267 key-transition-2014.txt
key-transition-2014.txt                          100% 3267   169.2KB/s   00:00
debug3: receive packet: type 96
[...]

ssh to all machines works like a charm.
Changing MTU or the tcp window scaling did not help. Switching from cable to
WiFi using the same router did not help.

Thaank you,
Giuseppe


-- System Information:
Debian Release: bookworm/sid
  APT prefers stable-updates
  APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'testing'), (500, 'stable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.15.0-2-amd64 (SMP w/8 CPU threads)
Locale: LANG=it_IT.UTF-8, LC_CTYPE=it_IT.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages openssh-client depends on:
ii  adduser           3.118
ii  dpkg              1.21.1
ii  libc6             2.33-1
ii  libedit2          3.1-20210910-1
ii  libfido2-1        1.9.0-1
ii  libgssapi-krb5-2  1.18.3-7
ii  libselinux1       3.3-1+b1
ii  libssl1.1         1.1.1l-1
ii  passwd            1:4.8.1-2
ii  zlib1g            1:1.2.11.dfsg-2

Versions of packages openssh-client recommends:
ii  xauth  1:1.1-1

Versions of packages openssh-client suggests:
pn  keychain      <none>
pn  libpam-ssh    <none>
pn  monkeysphere  <none>
pn  ssh-askpass   <none>

-- no debconf information