Cannot Ethernet tunnel with ssh on NetBSD 9

[Stephen Borrill]

I have two ends both with recent netbsd-9 and using base ssh/sshd:

OpenSSH_8.0 NetBSD_Secure_Shell-20190418-hpn13v14-lpk, OpenSSL 1.1.1g 21 Apr 2020

ssh for an interactive session works fine (and for things like rsync), but
as soon as I try to use L2 tunneling, it quickly dies with errors like:

sshd[1373]: fatal: channel 0: adjust 98329 overflows remote window 4294871838

Client-side I am using:
ssh -o Tunnel=ethernet -w 0:0 remotehost

Server-side sshd_config contains:
PermitTunnel ethernet

tap0 is a member of bridge0 as is a local LAN interface.

I think this is perhaps related to simply the amount of packets queued to
send over the tunnel. There are two LAN interfaces, one has an IP
address and is providing services such as web-proxy, the other is
used solely with vlan). Bridging to the quieter interface will run for
around 30s whereas the busy interface fails within a second.

[Michael van Elst]

Post by Stephen Borrill
ssh for an interactive session works fine (and for things like rsync), but
sshd[1373]: fatal: channel 0: adjust 98329 overflows remote window 4294871838

As a workaround try -oHPNDisabled=yes, that should disable the
window adjustments.

[Stephen Borrill]

Post by Michael van Elst

Post by Stephen Borrill
ssh for an interactive session works fine (and for things like rsync), but
sshd[1373]: fatal: channel 0: adjust 98329 overflows remote window 4294871838

As a workaround try -oHPNDisabled=yes, that should disable the
window adjustments.

I can confirm this works perfectly. Thanks Michael!