Re: Getting "write: address family not supported by protocol family" when using Restic over Tailscale

[Greg Troxel <gdt%lexort.com@localhost>]

Matti Andreas Kähäri <andreas.kahari%abc.se@localhost> writes:

> The KVM network is a bog standard IPv4-only thing that I haven't
> changed, and which other non-NetBSD guests are using without issue.

I note that you have declined to understand and explain what it is
doing.

>> > I would suggest running "ifconfig", understanding the results especially
>> > the address, ping and traceroute to your NAS.
>
> The _point_ of the Tailscale networking is to reach the NAS behind
> my home firewall (and CG-NAT).  There is a direct route through the
> Tailscale network, without going through any DERP server.

I understand the point.  You can't conclude from the intent that things
are 100% ok.

> eeyore% tailscale ping disco                                     
> pong from disco (100.102.136.126) via XXX.255.241.178:14032 in 5ms  
>
> Here, eeyore is the NetBSD system, and disco is the NAS,
> "XXX.255.241.178" is the visible IP of my home router, but since I'm
> behind a CG-NAT, I see a 100-something address on my router's actual WAN
> interface.

But not "ping", only "tailscale ping", which implies that your routing
tables aren't set up right, and there is some tailscale wrapper that is
[speculating now] doing some LD_PRELOAD of libc to replace the
networking syscall functions with somethingelse.

> I found a similar report from April in the pkgsrc-users list:
> https://mail-index.netbsd.org/pkgsrc-users/2026/04/28/msg042883.html
>
> There, it was rsync, not restic, that triggered the error.

Gueesing, this is probably a bug in tailscale.

> I can actually see some 500 (Internal Server Error) responses, and
> looking at the NAS logs, these corresponds to errors saying "Post
> request put error: unexpected EOF" (and the same, but with "rcat error"
> in place of "put error").
>
> It's "rclone serve restic" listening on the NAS.

Is it run under tailscale, or does tailscale work differently there?

>> >   "write: address family not supported by protocol family"
>> >
>> > I have a very dim memory of this happening either when writing via bpf
>> > or various tunnels, when they are configured for one address family and
>> > the packet written isn't right (or is interpreted as not right).
>
> Is it maybe chopping parts of the messages off?  Unfortunately, I don't
> really know the lower networking layers.

I would expect that a write would work or not.    But it is complicated,
and figuring out what's wrong is very likely to need understanding.