Time to Live (TTL) or hop limit, is a mechanism that limits the lifespan or life of data in networking, The designers of TCP/IP realizes that it would be possible for an IP packet to circulate endlessly on a network. For any given point to to point network R1 ends up sending the packet to R2 which thinks sending back to R1 is the right way to go will make the packet go, In simple point to point environment if the routers has an inappropriate instruction they could circulate