There are other techniques that Google's routers will most likely use to load-balance traffic transparently to multiple hosts. A relatively simple way is to has

There are other techniques that Google's routers will most likely use to load-balance traffic transparently to multiple hosts. A relatively simple way is to hash the (source, destination) address pair of the IP packet to determine which host to forward the packet to, so it doesn't necessarily require mirroring or any state. Only seamless failover when the host fails requires the fancy tricks.