Time To Live, TTL can be called the lifespan of an IP Packet! ( IPv4 )

• 8 Bit field on the IP Header, Max Value = 255 (All 1s ) set by the sender of the packet
• With each hop on the router or L3 device, the TTL gets reduced by one, before routing forward.
• Router receiving the packet with TTL = 1 discards the packet (as the TTL will be reduced to 0)
• Such a mechanism prevents the circulation of undeliverable packets in the network, thus ensures packets are not forwarded forever, in the case of routing loops.
• Additionally, router discarding the packet with TTL may ( not mandatory) send a ICMP Type 11, Code 0 ( Time to Live exceeded in Transit) to the source