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?
