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Openstack handling of DNS when using flat/private and floating/public IPs

Asked by Greg andrus

I need some clarification regarding DNS in Openstack when using both private and public addresses. If tenants use private addresses to communicate within the tenant but use public addresses with SNAT/DNAT to talk to other tenants, how is DNS typically set up to provide the correct forward and reverse lookups for both intra-tenant and inter-tenant communication.
We are looking at bringing Openstack into an existing environment, where the current DNS is outside the Openstack cloud.

Thank you.

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Gary Kotton (garyk) said : 		#1

A quantum subnet enables one to define to define the DNS servers for the specific subnet (https://wiki.openstack.org/wiki/QuantumV2APIIntro#Subnet). If the DNS server is on the private network then the request will be done via the private IP of the VM. If the DNS server is not on the subnet then the request will be done via the default gateway. In Quantum this can be the layer 3 agent which will do the NAT. That is, the source IP will be changed to the floating IP address.
So in your case the DNS requests willbe SNAT'ed (by the L3 agent). Pleas enote that there are some plugins that do not support the l3 agent and they do the management of the floating IP's (for example the NVP).
Thanks
Gary

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