Hi all,
It's been a while since I originally posted about this, and I've done a
lot of experimenting without landing on a working setup.
I'm trying to get a very simple test case working, where I have a number
of vnet interfaces, all configured with the link-local address
169.254.0.1/16, and have dnsmasq allocate the leases out of a different
range (in this case, I'm using a portion of the documentation prefix,
203.0.113.0/29). Here's my configuration:
pid-file=/var/lib/dnsmasq-vnet/dnsmasq-vnet.pid
bind-dynamic
interface=vnet*
log-dhcp
no-hosts
dhcp-range=203.0.113.0, 255.255.255.248, 1d
dhcp-option=option:router,169.254.0.1
shared-network=169.254.0.1,203.0.113.0
As far as I can tell, this is compliant with the directions given in the
manual section for shared-network. However, it doesn't work (no DHCP
offers are sent), and it gives the following logs:
Jul 10 15:37:02 server dnsmasq[314647]: started, version 2.84rc2
cachesize 150
Jul 10 15:37:02 server dnsmasq[314647]: compile time options: IPv6
GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack
ipset auth cryptohash DNSSEC loop-detect inotify dumpfile
Jul 10 15:37:02 server dnsmasq[314647]: warning: interface vnet* does
not currently exist
Jul 10 15:37:02 server dnsmasq-dhcp[314647]: DHCP, IP range 203.0.113.0
-- 255.255.255.248, lease time 1d
Jul 10 15:37:02 server dnsmasq[314647]: reading /etc/resolv.conf
Jul 10 15:37:02 server dnsmasq[314647]: using nameserver 127.0.0.53#53
Jul 10 15:37:02 server dnsmasq[314647]: cleared cache
Jul 10 15:37:08 server dnsmasq[314647]: listening on vnet0(#65):
169.254.0.1 port 53
Jul 10 15:37:09 server dnsmasq[314647]: listening on vnet0(#65):
fe80::fc54:ff:fe64:2291%vnet0 port 53
Jul 10 15:37:38 server dnsmasq-dhcp[314647]: no address range available
for DHCP request via vnet0
Jul 10 15:38:11 server dnsmasq-dhcp[314647]: message repeated 5 times: [
no address range available for DHCP request via vnet0]
Jul 10 15:38:19 server dnsmasq[314647]: stopped listening on vnet0(#65):
fe80::fc54:ff:fe64:2291 port 53
Jul 10 15:38:19 server dnsmasq[314647]: stopped listening on vnet0(#65):
169.254.0.1 port 53
The "listening on" and "stopped listening on" messages correspond to
when the guest VM is started and stopped, when the vnet0 interface is
created and destroyed. There is a start script for the VM which
automatically adds the required routes described in the manual section
for shared-network. (I'll likely move this to the dnsmasq dhcp-script
once the configuration is working.)
If I add the additional line:
dhcp-range=169.254.0.0, 255.255.0.0, 1d
it behaves essentially the same, with the addition of the rather
perplexing error message:
Jul 10 15:27:01 server dnsmasq-dhcp[313742]: DHCP range 169.254.0.0 --
255.255.0.0 is not consistent with netmask 255.255.0.0
(If I'm reading the manual page correctly, there shouldn't be any need
for the dhcp-range matching the interface on which the requests arrive,
but I thought I'd test it just in case.)
What's needed to make shared-network work?
Thanks in advance,
Paul
On 22/9/20 6:51 pm, Paul Gear wrote:
On 22/9/20 4:22 pm, Nicolas Cavallari wrote:
On 21/09/2020 21:32, Paul Gear wrote:
Hi all,
I've been trying to solve the same problem described in this blog post:
https://blog.fhrnet.eu/2020/03/07/dhcp-server-on-a-32-subnet/
In a nutshell, the situation is a VM host which performs routing and
firewalling for all its guests, providing an isolated IPv4 /32 (and in
my case an IPv6 /64 or /128 as well) to each VM guest, and using
interface routes on the host to direct traffic to each guest, without
wasting IPv4 addresses on /31 or /30 point-to-point links.
...
This sounds like the use case for shared-network:
shared-network=virbr13,192.168.1.26
or
shared-network=172.16.0.1,192.168.1.26
Alternatively, i sent this patch a while ago to be able to ignore any
matching, but my use case is different. I can send an updated version if
people are interested.
http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2018q1/012070.html
Ah, perfect - thanks very much, Nicolas.
I was doing my testing using the OS-packaged dnsmasq on my laptop, which
was 2.79. Looks like shared-network was added in 2.81. I'll upgrade
and do some testing, but it looks from the description like this is
exactly what I'm looking for.
Much appreciated.
Regards,
Paul
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