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 L3 Routing and NAT

Just like the core Quantum API provides abstract L2 network segments that are decopuled from the technology used to implement the L2 network, Quantum includes an API extension that provides abstract L3 routers that API users can dynamically provision and configure. These Quantum routers can connect multiple L2 Quantum networks, and can also provide a "gateway" that connects one or more private L2 networks to a shared "external" network (e.g., a public network for access to the Internet). See the section called “Use Case: Provider Router with Private Networks” and the section called “Use Case: Per-tenant Routers with Private Networks” for details on common models of deploying Quantum L3 routers.

The L3 router provides basic NAT capabilities on "gateway" ports that uplink the router to external networks. This router SNATs all traffic by default, and supports "Floating IPs", which creates a static one-to-one mapping from a public IP on the external network to a private IP on one of the other subnets attached to the router. This allows a tenant to selectively expose VMs on private networks to other hosts on the external network (and often to all hosts on the Internet). Floating IPs can be allocated and then mapped from one Quantum port to another, as needed.



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