I previously discussed using LISP to optimize your client-server traffic so today I’ll discuss the reverse direction: Egress Path Optimization from the Server to the Client. Let’s go over the need for Path Optimization in the direction from Server-to-Client with some pictures and explanations.
The Virtual Machine (VM) server is configured with a default gateway IP address, 192.168.1.1, which is the next hop IP address that the VM will forward packets towards as the traffic returns to the client outside the data center. In this data center environment, we’ve deployed the default gateway using the First Hop Redundancy Protocol (FHRP). In reality, FHRP is an umbrella technology term that includes Hot Standby Routing Protcol (HSRP) and Virtual Router Redundancy Protocol (VRRP), two main technologies that provide transparent failover and redundancy at the first hop IP router. Please see info on FHRP here.
Also notice that the VM default gateway is the same as the HSRP Virtual IP Address (VIP). The HSRP VIP binds itself to one of the physical HSRP Routers via an HSRP election process using Layer 2 control packets between the two physical HSRP Routers and this means that the VM default gateway, since it points to a VIP, may move between physical HSRP Routers, and of course which is then intent and design when using any type of FHRP.
In the above picture, the Path is Optimized from Server to Client, so now let’s take a look at what happens when we migrate the VM to the new data center.