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Re: network config not working on newer libvirt



Greetings LAine,

> When you say "the vm", you mean the one running libreelec, that is
> trying to get and IP address, correct?

yes, you are correct.

> I guess Broadcom.home is the IP of the VM that's running the dhcp
> server? (I should have suggested using "tcpdump -n -e -v" :-/)
>

frankly, I have no idea who is Broadcom.home.
here is the requested dump: https://dpaste.com/849DMX9ND

> It looks strange, but is normal. What usually happens is this:
>
> 1) The guest sends a DHCP Discover Request, suggesting that it would
> like to use the addres 10.0.0.40 (These details will be revealed once
> you add "-v" to your tcpdump commandline.
>
>
> 2) The DHCP server says to itself "Hmm, this guy wants to use 10.0.0.40,
> which is okay with me, but first I should see if someone else is using
> it", so it sends out an ARP request for 10.0.0.40. Then just to be sure,
> it sends another.
>
> (at this point, if the server is dnsmasq and it hasn't received an ARP
> request, for some reason it sends an ICMP echo request to 10.0.0.40 (the
> requested/suggested IP) with destination MAC address of the client that
> just sent the DHCP request. No idea why. It won't be answered though
> (unless the client actually still had a lease on that address and was
> just renewing; but the DHCP server would know it if that's what was
> happening, so...)
>
> 3) If the server doesn't receive any response to the ARP request, then
> it will send a DHCP response to the requested IP + client MAC saying
> "Yes, you can use that IP address.
>
> 4) I'm not sure why (because it's been > 20 years since I last read the
> DHCP RFC), but in the case I just looked at on my host (which is using
> dnsmasq as the server, and dhclient as the client), the same request and
> response are sent/received at the same IP+MAC addresses a 2nd time.
>
> 5) at this point everybody agrees on the new IP address, the client sets
> its IP address, the server updates its leases table, and life carries on.
>
> But to back up for a minute - it's completely normal for the DHCP server
> to send out an ARP request and get no response. I think things are going
> south sometime after that. Are you seeing a DHCP reply at all? If you
> don't see it on the libreelec (client) machine's tap device, check if
> you see it going *out* on the DHCP server's tap. If it's not there, then
> you'll need to debug inside the guest running the DHCP server.
>
> Before this packet is receivd, the guest doesn't yet know that's its IP
> address, but it does know that's its MAC address, and it's waiting for a
> DHCP reply, so it takes the info from the reply, then sends another
> request, this time including all the options it received in the first reply.
>
> 4) Now
>
>
should I add another nic with static ip and try to trace the pkts from there?



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