[Qemu-devel] IP mismatch in redirection using user-net dhcp

[Qemu-devel] IP mismatch in redirection using user-net dhcp

[Yann Dirson]

For some as-yet-unknown reason, the IP assigned by the user-net DHCP
server occasionally switches to 10.0.2.16.  I suspect this happens while
renewing the lease while I'm away, since that would explain why the
headless VM is unreachable when I come back on mondays - then when booting
with SDL display, I find out the IP is 10.0.2.16.

This would not be a problem at all, if the port redirections would know
about that, but a tcpdump in the VM shows that my "-redir
tcp:10080::10080" is indeed taken as "tcp:10080:10.0.2.15:10080", even
though the attributed IP is 10.0.2.16.  Not sure how qemu could be taught
to do something sensible here, without breaking multi-NIC setups.

But with some luck we should not have to bother with it, if only the
problem is just that the lease renewal is broken.


Bringing the (gentoo/dhcpcd) VM back on its feet seems to require all of
the following steps, which is quite error-prone (and time-consuming when a
single step is missed;):
- "dhcpcd -k", which clears /var/cache/dhcpcd-eth0.cache
- removing /var/lib/dhcpc/*
- restarting qemu itself so that it forgets about the lease as well

Would it make sense to be able to tell qemu "do not ever issue a lease on
an IP different from 10.0.2.15", and possibly make that the default for
single-NIC VMs ?

-- 
Yann Dirson <ydirson@altern.org>
             <dirson@debian.org>

Re: [Qemu-devel] IP mismatch in redirection using user-net dhcp

[Paul Brook]

> Would it make sense to be able to tell qemu "do not ever issue a lease on
> an IP different from 10.0.2.15", and possibly make that the default for
> single-NIC VMs ?

You could tie the IP to the MAC address. Ie. make the dhcp code discard the 
previous lease if it gets another request from the same MAC address. This 
should work for all setups.

Paul