[Dnsmasq-discuss] SUCCESS

[Gene Czarcinski]

On 10/16/2012 03:51 PM, Simon Kelley wrote:
> OK. I committed a variation on your code, which makes --listen-address 
> work with DHCPv6. This was definitely bugged before, and is sensible 
> now. Thanks.
I do not believe that it was either --listen-address or --interface.  I 
believe that the old code was incorrectly checking for them.  The 
important thing is the subnetwork defined the the --dhcp-range 
specification and which device has that subnetwork. The only good thing 
the iface_check() did was to test for one of the two exclude lists with 
the other being checked by dhcp6_packet() itself.

I believe that this same situation ("problem") exists in dhcp_packet() 
but it has some slightly different code paths so it ends up working.

As I was writing this, I thought of an interesting (possible problem) 
"feature".  I believe that with the new dhcp6 code, that you could have 
dhcp6 service without any --interface or --listen-address ... you just 
cannot have that interface on an exclude list.

>
>
> BUT
>
> I thought about this and checked back through some earlier fixes, and 
> found this.
>
> https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1013529
>
> which refers to exactly the same situation you're working with, but in 
> OpenStack.
>
> The important take-home is that to make DHCP work with multiple 
> instances of dnsmasq, each dealing with a single interface, it's 
> necessary to set SO_BINDTODEVICE on the DHCP socket to associate it 
> with a particular interface. The patch which went in around 2.61 - 
> 2.62 does just that, provided that there is exactly one --interface 
> parameter. It doesn't work with --listen-address.
>
> So, to make libvirt work correctly in all circumstances, it will need 
> to use --interface, and NOT --listen-address. This applies to DHCPv4 
> as well as DHCPv6.
Now this I do not understand.  While libvirt does not currently support 
dhcp6, it does support dhcp4 and runs one copy of dnsmasq for each 
virtual network.  I am pasting in a typical command line as shown by "ps 
ax".  Yes, everything is on the command line.  One of these days, if I 
feel ambitious enough, I am going to change it to put everything into a 
conf file and maybe add a --con-dir so that you could test some stuff 
without standing on your head ... rebuilding the libvirt rpms takes a 
little time.


---- I broke the text up to multi line so it is readable 
--------------------------------
/sbin/dnsmasq --strict-order --bind-interfaces --domain=virt 
--local=/virt/ \
--domain-needed --pid-file=/var/run/libvirt/network/default.pid \
--conf-file= --except-interface lo \
--listen-address 192.168.122.1 --local=/122.168.192.in-addr.arpa/ \
--dhcp-range 192.168.122.2,192.168.122.254 \
--dhcp-leasefile=/var/lib/libvirt/dnsmasq/default.leases \
--dhcp-lease-max=253 --dhcp-no-override --expand-hosts
--------------------------------------------------------------------------------------------------

Comments?
>
> Gene, I'm hoping you can act as the conduit for this information to 
> the libvirt community. It's a tough job, etc, etc.
Tell me about it.

Gene