Provider Network DHCP

asked 2017-11-14 08:27:54 -0500

stackopen gravatar image

Hi all,

I come from a vSphere environment and started to test openstack. I deployed 4 Nodes ( 1 Controller + 3 Compute) using packstack and I managed to setup networking similar to vSphere by using VLANs. So the openstack controller node and Compute nodes are connected via br-ex:bond0 using vlans to our existing network. Of course there are already DNS and DHCP servers on this network (all windows based). By creating the subnets in neutron I first disabled DHCP but If I recall correctly this is necessary for the instances to use cloud-init. So for testing I enabled the DHCP and allocated a few free IPs which are excluded from our Windows DHCP. I thought maybe the DHCP (dnsmasq) is somehow isolated and only accepts DHCP requests from instances but looking at /var/log/messages I can see all machines can reach the DHCP on the openstack network controller:

Nov 13 13:15:02 gedaspl03 dnsmasq-dhcp[6116]: DHCPREQUEST(tapf01d75bb-1e) 00:50:56:b7:0f:36 Nov 13 13:15:02 gedaspl03 dnsmasq-dhcp[6116]: DHCPNAK(tapf01d75bb-1e) 00:50:56:b7:0f:36 lease not found

So far no non openstack machines have acquired any of the pre allocated IPs from dnsmasq yet. Is it possible to have dnsmasq running besides other DHCP servers?

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dnsmasq won't send positive acknowledgments. If the NAKs concern you, you can try configuring it to ignore requests entirely by setting its ignore option. You can set your own dnsmasq options with the dhcp_agent.ini parameter dnsmasq_config_file.I never tried this though.

Bernd Bausch gravatar imageBernd Bausch ( 2017-11-14 16:20:30 -0500 )edit

Hi Bernd, thanks a lot for your quick answer and sorry for my late reply. So this means I can use both DHCPs? The messages are only informational and dnsmasq will not handle the requests from non openstack instances?

stackopen gravatar imagestackopen ( 2017-11-21 07:10:14 -0500 )edit

I am not a networking expert, but it seems that the experts agree: DHCP servers that are serving the same subnet should not have a single “shared” scope, but rather they should have a “split” scope.

Bernd Bausch gravatar imageBernd Bausch ( 2017-11-21 17:45:47 -0500 )edit

If your OpenStack DHCP servers use addresses that are excluded from the datacenter's DHCP servers, that is a split scope.

Bernd Bausch gravatar imageBernd Bausch ( 2017-11-21 17:49:07 -0500 )edit