Re: network config not working on newer libvirt

On 9/4/20 12:38 AM, daggs wrote: You haven't said which distro, nor what is the libvirt exact libvirt version (probably won't matter in this case, but in general "libvirt x.y.z" is more useful than "latest stable libvirt"). If you have full connectivity once you've manually assigned IP addresses, then you don't have any routing problems, so that can be counted out. (Anyway, DHCP packets never go beyond the local network). In that case, you've most likely either got a firewall problem on host or guest, or a problem with your dhcp server. From where? The host? or the guests? Your config is for a bridge that's created by libvirt, but with no iptables rules, no dnsmasq instance, and no IP address on the host. So any DHCP server config is outside libvirt's realm, as are any iptables or nftables rules, so in this case there is nothing to look at in the libvirt config for either of these issues. I would start troubleshooting by making sure that the dhcp server is running, and that you can communicate between the machine with DHCP server and the guest once a manual IP is assigned. Then use tcpdump or wireshark at different places on the path between those two to see how far the DHCP request is getting out, whether a response is being sent by the server, and if so how far the response is getting back (i.e. on the host, run tcpdump on the guest's tap device; if you see the DHCP request there, then run tcpdump on the bridge, if you see it there, run it on the tap device for the guest, if you see it there, then run tcpdump inside the guest; then check the dhcp server logs to see if it's receiving requests. While you're doing all of this, you can also be noticing whether or not a DHCP response is arriving at each step (and if you see the response, you can skip looking further ahead in the packet path, since you know by inference that it made it all the way to the DHCP server). Once you find the point that the packet is blocked, you'll be better able to determine why.