NVO3 participants: Tom Herbert brought up that the L3 address migration should be discussed in the NVO3 mobility draft (now called NVO3-ts-address-migration). As David Black pointed out in his email that L3 address migration is similar to L2 migration causing one subnet being spread across many.
The outbound traffic of fragmented L3 addresses doesn't have the same issue as L2 address migration, but the inbound traffic has the same issues as L2 address migration. I added one small section to describe the L3 Address Migration. Please provide comments or suggestions. ------------------------------ L3 Address Migration When the attachment to NVE is L3 based, TS migration can cause one subnetwork to be scatted among many NVEs, or fragmented addresses. The outbound traffic of fragmented L3 addresses doesn't have the same issue as L2 address migration, but the inbound traffic has the same issues as L2 address migration (Section 6). In theory, host hosting at DCBR can achieve the optimal path forwarding in very fragmented network. But host routing can be challenging in a very large and highly virtualized data center, there could be hundreds of thousands of hosts/VMs, sometimes in millions, due to business demand and highly advanced server virtualization technologies. Optimal routing of TS's inbound traffic. This means that as a given TS moves from one server to another, the (inbound) traffic originated outside of the TS's directly attached NVE, and destined to that TS be routed optimally to the NVE to which the server presently hosting that TS, without first traversing some other NVEs. This is also known as avoiding "triangular routing". In theory, host hosting by every NVE (including the DCBR) can achieve the optimal path forwarding in very fragmented network. But host routing can be challenging in a very large and highly virtualized data center, there could be hundreds of thousands of hosts/VMs, sometimes in millions, due to business demand and highly advanced server virtualization technologies. ECMP can be used by the DCBR or any NVEs that don't support host routing or can't access NVA to distribute traffic equally to any of the NVEs that support the subnet (VN). If an NVE doesn't have the destination of a data packet directly attached, it can query NVA for the target NVE to which the destination is attached, and encapsulate the packet with the target NVE as outer destination before sending it out. Another approach is to designate one or two NVEs as designated forwarder for a specific subnet when the subnet is spread across many NVEs. For example, if high percentage of TSs of one subnet is attached to NVE "X", the remaining small percentage of the subnet is spread around many NVEs. Designating NVE "X" as the designated forwarder for the subnet can greatly reduce the "triangular routing" for the traffic destined to TSs in this subnet. Linda Dunbar
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