53VLT Proxy GatewayThis chapter describes the VLT Proxy Gateway feature.Proxy Gateway in VLT DomainsThe functionality to configure the proxy gateway in VLT domains is supported on the S4810, S4820T,S6000, Z9000 platforms.You can configure a proxy gateway in VLT domains. A proxy gateway enables you to locally route thepackets that are destined to L3 endpoint of the other VLT domain. Therefore, the VLT peers of onedomain can route the L3 packets destined for VLT peers of another domain as long as they havereachability for those IP destinations. This will avoid sub-optimal routing of sending the packets to theactual VLT domain and routing them from there, in case the received packets are destined for theendpoint of the other VLT domain. It also provides resiliency in case of VLT peer going down on one VLTdomain by performing the proxy routing for that peer’s DA MAC by the other VLT domain.The typical scenario is virtual movement of servers across data centers. Virtual movement enables livemigration of running virtual machines from one host to another without a downtime. Consider a squareVLT connecting two data centers. If a VM, say VM1 on Server Rack 1 has C as its default gateway and VM1performs a virtual movement to Server Rack 2 with no change in default gateway, then L3 packetsdestined for C can be routed either C1 or D1 locally. This behavior is achieved by installing the local_DAentries for C/D in C1/D1 so that the packets for C/D could have a hit at C1/D1 and routed locally.In the following figure, server racks, named Rack 1 and Rack 2 are part of data centers, named DC1 andDC2 respectively. Rack 1 is connected to devices A and B in Layer 2. Similarly, Rack 2 is connected todevices A and B in Layer 2. A VLT LAG is present between A and B. A and B are connected to core routers,C and D. VLT routing is present between C and D. C1 and D1 are Layer 3 routers in DC2 and they areconnected with core routers, C and D. The core or Layer 3 routers are then part of a Layer 3 cloud.VLT Proxy Gateway 869
