[Dnsmasq-discuss] dhcp entries not being removed from dnsmasq

Simon Kelley simon at thekelleys.org.uk
Wed May 17 19:34:47 BST 2017

You're assuming a lot of knowledge of OpenStack which is strictly
off-topic here.

Given that,  a couple of observations.

1) If dnsmasq is getting a DHCPELEASE packet, it will log that. Given
you're not seeing that in logs, then either dhcp_release is not being
invoked, or it's getting the wrong parameters, or it's failing. Can you
see the DHCPRLEASE messages in your packet dump?

2) What dhcp client is openstack using? Some DHCP servers will continue
to use a previous address if they fail to contact a DHCP server.


On 17/05/17 17:24, Graeme Peterson wrote:
> Hi all.
> Sorry if this issue has been discussed and resolved, I am new to the
> list. I tried to find it in the list, and came across this reference to
> the issue from Jan 2016:
> http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2016q1/010273.html
> What I am seeing is with OpenStack Newton on Ubuntu 16.10
> (4.8.0-49-generic), with force_dhcp_release=True in /etc/nova/nova.conf,
> using tcpdump on the netns for the relevant Openstack network, I see
> dnsmasq receives the dhcp request, issues an IP, and that IP should be
> released (Openstack should be calling dhcp_release, I need to figure out
> how to verify that it is or is not happening, however
> force_dhcp_release=True is explicitly set in /etc/nova/nova.conf) , but
> it seems like the dhcp entry isn't being entirely released. The odd
> thing is that when a new VM wants an IP, tcpdump shows the request
> coming in for an address, but no reply, and OpenStack thinks it got an
> IP - the same one that used to belong to the recently terminated VM -
> but there is no dhcp offer in the tcpdump, and the dnsmasq log shows:
> May 16 16:53:15 dnsmasq-dhcp[40394]: 3306068020
> DHCPREQUEST(tapc5399cce-70) fa:16:3e:8e:83:97
> May 16 16:53:15 dnsmasq-dhcp[40394]: 3306068020 tags: tag0, known,
> tapc5399cce-70
> May 16 16:53:15 dnsmasq-dhcp[40394]: 3306068020 DHCPACK(tapc5399cce-70)
> fa:16:3e:8e:83:97 host-132-16-0-13
> ...
> ...
> ...
> May 16 16:57:12 dnsmasq-dhcp[40394]: 461988430 available DHCP subnet:
> May 16 16:57:12 dnsmasq-dhcp[40394]: not using configured address
> because it is leased to fa:16:3e:8e:83:97
> May 16 16:57:12 dnsmasq-dhcp[40394]: 461988430
> DHCPDISCOVER(tapc5399cce-70) fa:16:3e:31:de:d3 no address
> available
> I don't see a log entry for a release of, not sure if there
> should be one.
> Is this a known and hopefully fixed issue? Can I provide further info to
> help investigate it?
> Thanks,
> Graeme
> _______________________________________________
> Dnsmasq-discuss mailing list
> Dnsmasq-discuss at lists.thekelleys.org.uk
> http://lists.thekelleys.org.uk/mailman/listinfo/dnsmasq-discuss

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