[Dnsmasq-discuss] possible Bug: DHCPDISCOVER no address available

[Thomas Kärgel]

Hi everyone,

Thanks for the wonderful work you did in this project. i'm using dnsmasq
for years now and never had any problems with it until now. I hope that
someone can help us with this problem or at least help us pointing out
what the cause of this problem is. Many thanks in advance.

 Dnsmasq is used as DHCP-Server in Openstack Cloud Software. The normal
usage principle looks like this:

1. An Openstack service starts dnsmasq as DHCP-daemon configured with
"--dhcp-hostsfile=filename"-option. The hostsfile is written by
openstack and filled with information in dnsmasq-format.
Example:
fa:16:3e:86:19:a6,,10.72.226.10,172800
fa:16:3e:78:19:8b,,10.72.226.11,172800

2. everytime a new entry is added or removed in the hostsfile dnsmasq
gets signal HUP sent by Openstack, so that it re-reads its configs and
hostfile. After that dnsmasq is aware of the mac-address/IP-pair and can
deliver the IP when the client performs DHCP-Discover.

The above mechanism is working fine in most cases. But lately there were
a few reports (4 afaik) that this mechanism is not working entirely
reliable.
Dnsmasq re-reads it's configs but still claims that no address is
available for the specific mac-address, while other clients are still
receiving their adresses fine.
The new entries in hostsfile do not get served until dnsmasq is killed
and restarted.

Things i checked so far:
-new hostsfile is completely written to disk at the time dnsmasq gets
signal HUP.
-no firewall rules or whatever interfere the communication between
dnsmasq and its client.
-manually sigHUPing dnsmasq has no effect. Dnsmasq logs that it has
re-read config files including hostsfile.
-concerned entries in hostsfile are valid (and work as soon as dnsmasq
is killed and restarted)

Details:

Used dnsmasq version is 2.59. The issue was recognized on Ubuntu
12.04LTS and SLES11SP2 systems. Upgrading to dnsmasq 2.66 had no effect.
The issue still occurs.

Dnsmasq is started with the following parameters in my openstack
environment. (This may look slightly different on other environments):
ps aux|grep dnsmasq
dnsmasq   8123  0.0  0.0  11112  1036 ?        S    May10   8:39
/usr/sbin/dnsmasq --log-dhcp --no-hosts --no-resolv --filterwin2k
--strict-order --bind-interfaces --interface=ns-606c17e0-c3
--except-interface=lo --domain=openstacklocal
--pid-file=/var/lib/quantum/dhcp/e4d06a35-c14c-4102-88bc-4be760927b94/pid --dhcp-lease-max=2000
--dhcp-hostsfile=/var/lib/quantum/dhcp/e4d06a35-c14c-4102-88bc-4be760927b94/host
--dhcp-optsfile=/var/lib/quantum/dhcp/e4d06a35-c14c-4102-88bc-4be760927b94/opts
--dhcp-script=/usr/bin/quantum-dhcp-agent-dnsmasq-lease-update
--leasefile-ro --dhcp-range=set:tag0,10.72.0.0,static

There is a thread on openstack mailing-list that describes this behavior
in all details:
https://lists.launchpad.net/openstack/msg23817.html
Most of the information there is openstack specific. I think it is of no
interest here.

An excerpt of relevant log entries looks like this:
May 20 09:01:40 grizzly-236 dnsmasq-dhcp[7235]: read
/var/lib/quantum/dhcp/e6f27330-be41-478c-b4d2-49ed4ce0af00/host
May 20 09:01:40 grizzly-236 dnsmasq-dhcp[7235]: read
/var/lib/quantum/dhcp/e6f27330-be41-478c-b4d2-49ed4ce0af00/opts
DHCPDISCOVER(tapdbcef145-f5) fa:16:3e:2d:0d:e0
May 20 09:02:19 grizzly-236 dnsmasq-dhcp[7235]:
DHCPOFFER(tapdbcef145-f5) 10.20.30.2 fa:16:3e:2d:0d:e0
May 20 09:02:19 grizzly-236 dnsmasq-dhcp[7235]:
DHCPREQUEST(tapdbcef145-f5) 10.20.30.2 fa:16:3e:2d:0d:e0
May 20 09:02:19 grizzly-236 dnsmasq-dhcp[7235]: DHCPACK(tapdbcef145-f5)
10.20.30.2 fa:16:3e:2d:0d:e0 10-20-30-2
May 20 09:04:34 grizzly-236 dnsmasq-dhcp[2190]:
DHCPDISCOVER(tapdbcef145-f5) 10.0.2.15 fa:16:3e:fc:1f:9a no address
available
May 20 09:04:52 grizzly-236 dnsmasq-dhcp[2190]:
DHCPDISCOVER(tapdbcef145-f5) 10.0.2.15 fa:16:3e:fc:1f:9a no address
available


Best regards,
Thomas



-- 
Thomas Kärgel
Linux Consultant
Mail: kaergel at b1-systems.de
B1 Systems GmbH
Osterfeldstraße 7 / 85088 Vohburg / http://www.b1-systems.de
GF: Ralph Dehner / Unternehmenssitz: Vohburg / AG: Ingolstadt,HRB 3537

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 554 bytes
Desc: OpenPGP digital signature
URL: <http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/attachments/20130523/80488a68/attachment.pgp>