I’m not sure I wrote about the taxonomy of numerous virtual networking implementations. Just in case, here it is ;)
Layer-2 or layer-3 networks?
Some virtual networking solutions emulate thick coax cable (more precisely, layer-2 switch), giving their users the impression of having regular VLAN-like layer-2 segments.
Examples: traditional VLANs, VXLAN on Nexus 1000v, VXLAN on VMware vCNS, VMware NSX, Nuage Networks Virtual Services Platform, OpenStack Open vSwitch Neutron plugin.
Other solutions perform layer-3 forwarding at the first hop (vNIC-to-vSwitch boundary), implementing a pure layer-3 network.
Examples: Hyper-V Network Virtualization, Juniper Contrail, Amazon VPC.
Layer-2 networks with layer-3 forwarding
Every layer-2 virtual networking solution allows you to implement layer-3 forwarding on top of pure layer-2 segments with a multi-NIC VM.
Some virtual networking solutions provide centralized built-in layer-3 gateways (routers) that you can use to connect layer-2 segments.
Examples: inter-VLAN routing, VMware NSX, OpenStack
Other layer-2 solutions provide distributed routing – the same default gateway IP and MAC address are present in every first-hop switch, resulting in optimal end-to-end traffic flow.
Layer-3 networks and dynamic IP addresses
Some layer-3 virtual networking solutions assign static IP addresses to end hosts. The end-to-end layer-3 forwarding is determined by the orchestration system.
Example: Amazon VPC
Other layer-3 virtual networking solutions allow dynamic IP addresses (example: customer DHCP server) or IP address migration between cluster members.
Examples: Hyper-V network virtualization in Windows Server 2012 R2, Juniper Contrail
Finally, there are layer-3 solutions that fall back to layer-2 forwarding when they cannot route the packet (example: non-IP protocols).
Example: Juniper Contrail
A picture is worth a 1000 words
Why does it matter?
In a nutshell: the further away from bridging a solution is, the more scalable it is from the architectural perspective (there’s always an odd chance of having clumsy implementation of a great architecture). No wonder Amazon VPC and Hyper-V network virtualization (also used within the Azure cloud) lean so far toward pure layer-3 forwarding.
- Watch the Overlay Virtual Networking webinar (and the Following Packets across Overlay Virtual Networks addendum).
- Check out cloud computing and networking webinars and webinar subscription.
- Use ExpertExpress service if you need short online consulting session, technology discussion or a design review.