LISP Mobility with OTV
In previous posts we talked about implementing OTV with ASR routers. OTV is a overlay network to get end-to-end layer 2 connections over a layer 3 (WAN) network. In most implementations is FHRP (First Hop Redundancy Protocol, like HSRP/VRRP) filtering needed. These filters are needed to keep routing in the same datacenter where the traffic originates.
Let’s take another look at the high level design:
When FHRP filtering is active, the Virtual IP (aka.. default gateway for clients) is active in both datacenters. Which means: a packetflow from a server in DC1 is routed on the core switch/router in DC1. If you move (vMotion/ live migrate) that server to DC2, the packetflow is routed on the switch/router in DC2.
If you think this through, the datacenter outgoing trafficflows are efficient: routing will be done on the most nearby router. But… incoming traffic from branch offices is still not efficient: the WAN network does not know where the VM is hosted, so the packets are routed by the normal routing protocols. This could result in inefficient routing: if the IP range is routed to DC1 on the WAN and the VM is hosted in DC2, the Datacenter-Interconnect (OTV) will be used to get the packets to the VM.
This is where LISP mobility comes in.