network config not working on newer libvirt

daggs daggs at gmx.com
Fri Sep 4 22:47:27 UTC 2020


Greetings Laine,

> >
> > 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.
> >
> >
>
> alright, I'll try that, thanks.
>

I've ran tcpdump on the vm's tap device, here is what I see:
01:42:15.404754 IP 0.0.0.0.bootpc > 255.255.255.255.bootps: BOOTP/DHCP, Request from 52:54:00:5a:4c:8c (oui Unknown), length 548
01:42:15.405075 IP Broadcom.Home.bootps > 10.0.0.40.bootpc: BOOTP/DHCP, Reply, length 300
01:42:15.735893 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:6b:1b:92.8003, length 35
01:42:17.718941 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:6b:1b:92.8003, length 35
01:42:17.846918 IP6 fe80::fc54:ff:fe5a:4c8c > ff02::2: ICMP6, router solicitation, length 16
01:42:19.702944 STP 802.1d, Config, Flags [none], bridge-id 8000.52:54:00:6b:1b:92.8003, length 35
01:42:20.450441 ARP, Request who-has 10.0.0.40 tell Broadcom.Home, length 28

I think that issue is this:
01:42:20.450441 ARP, Request who-has 10.0.0.40 tell Broadcom.Home, length 28

I'm not sure if this is expected but looks like my dhcp server ignores it.
any thoughts on the matter?

Dagg.





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