Re: Diagnosing virtual machine network issues

Hi Rodney,

> On Aug 10, 2024, at 9:11 AM, Rodney W. Grimes <freebsd-rwg@gndrsh.dnsmgr.net> wrote:
> 
>> 
>> 
>>> On Aug 2, 2024, at 5:58?PM, Bakul Shah <bakul@iitbombay.org> wrote:
>>> 
>>> On Aug 2, 2024, at 3:52?PM, Alex Arslan <ararslan@comcast.net> wrote:
>>>> 
>>>>> Just a comment and a name server line:
>>>>> 
>>>>> $ cat /etc/resolv.conf
>>>>> # Generated by resolvconf
>>>>> nameserver 192.168.122.1
>>>> 
>>>> I believe that is the host IP, so I guess the VM is using the host for DNS
>>>> resolution? Interestingly, if I add `nameserver 8.8.8.8` below the line
>>>> with the host IP, it takes 10 seconds rather than 30 to reach the expected
>>>> domain resolution failure. If I put 8.8.8.8 above the host IP, the domain
>>>> resolution failure is instantaneous.
>>> 
>>> What does your host use as a namesever?
>> 
>> The nameserver is 127.0.0.53. It sets options edns0 and trust-ad, and
>> includes a search entry as well.
> 
> First, is that a typo and you mean 127.0.0.1:53?

No, the host's /etc/resolv.conf has `nameserver 127.0.0.53`, I just went
back and rechecked to be sure.

> Second, is that name server locked to 127.0.0.1, or is it
> actually listinging on *:53?  If it is LOCKED you have no name server
> running on 192.168.122.1 to be reached by the VM, if it is NOT locked
> can the guest ping 192.168.122.1, and can it reach dns at that IP on
> port 53?   Can the host send a packet BACK to the guest?

I apologize but I don't really know enough about these things to know how
to answer your question. I did post the output of tcpdump on the VM and
the host a while back but that was for the invalid request, so that
probably doesn't capture what you're describing.

> Third you can "fix" the "nameserver 192.168.122.1" entry in /etc/resolv.conf
> by configuring the DHCP server that handed out the lease to the VM to send
> a namserver entry of 8.8.8.8.

If I understand correctly, that is indeed what we've done as a Band-Aid fix
for the time being: I added the line `prepend_nameservers=8.8.8.8` to
/etc/resolvconf.conf.

>> 
>>> 
>>>> Not a particularly satisfying conclusion to this saga as I don't understand
>>>> why it's happening but at least I have a workaround that should hopefully
>>>> do the job. I really appreciate everyone's help and input thus far!
>>>> 
>>>> What's the best way to add `nameserver 8.8.8.8` to /etc/resolv.conf as
>>>> part of the VM's configuration?
>>> 
>>> You should diagnose the problem of the nameserver at 192.168.122.1
>>> and fix it to act properly. I don't use vm (just bhyve) so can't help
>>> you with its config.
>> 
>> I do still plan to try to figure out what the actual issue is, but I also
>> now have a path forward in the meantime. :)
>> 
>> 
> 
> -- 
> Rod Grimes                                                 rgrimes@freebsd.org <mailto:rgrimes@freebsd.org>