How does Neutron implement overlapping IPs?

asked 2013-09-25 05:35:12 -0500

anonymous user


updated 2013-09-25 09:41:26 -0500

darragh-oreilly gravatar image

How openstack allows tenants to choose their own IP addressing scheme, even if those IP addresses overlap with those used by other tenants.

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answered 2013-09-25 10:05:50 -0500

darragh-oreilly gravatar image

Any layer-2 plugin provides total isolation between L2 networks, so there is no problem there.

Some plugins use the l3-agent for routing, SNAT gateway and floating IPs. It uses Linux IP namespaces to isolate Neutron routers running on the same node. So each router has its own interfaces, route table and iptables rules, all within its own IP namespace. Subnets connected to the same Neutron router can not have overlapping IP ranges.

The Neutron metadata agent queries the Neutron server with the instance's source IP addresses and the router-id to determine which instance is making the call before proxying the request to nova-metadata.

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Thanks for the answer. Would you be able to elaborate a bit more on how the routing is done to different namespaces? Suppose that 1 network node has 2 Neutron routers with same IP address, each running in different namespaces. How does network node know which router it should route to?

l2edzl3oy gravatar imagel2edzl3oy ( 2015-01-20 00:05:56 -0500 )edit

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Asked: 2013-09-25 05:35:12 -0500

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Last updated: Sep 25 '13