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:

> This is the network configuration for the guests as seen with "virsh
> net-edit default":
>
> <network>
>   <name>default</name>
>   <uuid>9aee69db-b83c-4d96-9f79-1155b3a71030</uuid>
>   <forward mode='nat'/>
>   <bridge name='virbr0' stp='on' delay='0'/>
>   <mac address='52:54:00:ce:24:79'/>
>   <ip address='192.168.122.1' netmask='255.255.255.0'>
>     <dhcp>
>       <range start='192.168.122.100' end='192.168.122.200'/>
>     </dhcp>
>   </ip>
> </network>
>
> What else can I tell you?  I have most centainly failed (not declined)
> to undrestand, so please enlighten me about what further info I should
> supply, and how.

Run ifconfig on the guest, and on the host.  There are (at least) two
ways to provide networking to guests.  One is to bridge the guests
(virtual) network interface to the (real) network interface of the host.
Then the guest appears to be on the same LAN segment as the host, probably
gets an address from the same DHCP sever, probably uses the same router,
etc.

The other approach is to make the host a router, and to do
forwarding/nat and maybe firewall.

I'm not familiar with KVM specifically and more importantly the
management practices surrounding it; I mostly use Xen.   But reading
your xml, it says "nat" and there's an address 192.168.122.1 which is
probably for the hosts virtual interface that's on the same virtual
ethernet as the guest, and probably the guest does DHCP to a server on
the host and gets an address within 100-200.

Using ifconfig, or however Linux spells that, will tell you what
interfaces there are and what addresses are on them.

This is probably not your problem, but I think it's always good to
understand your network topology.

>> > 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.
>
> Sure, I can ping:
>
> eeyore% ping -c 4 disco
> PING disco.my-ts-domain.ts.net (100.102.136.126): 56 data bytes
> 64 bytes from 100.102.136.126: icmp_seq=0 ttl=64 time=6.108598 ms
> 64 bytes from 100.102.136.126: icmp_seq=1 ttl=64 time=6.227608 ms
> 64 bytes from 100.102.136.126: icmp_seq=2 ttl=64 time=5.782858 ms
> 64 bytes from 100.102.136.126: icmp_seq=3 ttl=64 time=5.395658 ms
>
> ----disco.my-ts-domain.ts.net PING Statistics----
> 4 packets transmitted, 4 packets received, 0.0% packet loss
> round-trip min/avg/max/stddev = 5.395658/5.878680/6.227608/0.372874 ms

Is that going through tailscale, or not?   In a normal VPN, there's a
route into a VPN interface for things reachable via the VPN.  tailscale
appears to have a different plan?

traceroute will likely shed light on this.

>> > 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.
>
> Possibly, or in Go on NetBSD.

Fair point, likelihood hard to assess.

>> > 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?
>
> On the NAS, Tailscale is running.  The rclone service listens to all
> available addresses of the system, including the Tailscale addresses.

"tailscale addresses" means what?  Is there some part of RFC1918 address
space assigned (in your setup) to tailscale?  Do they work with real
syscalls, and no wrappers?  Why is that different on your netbsd kvm
guest?