Time to Live field in IP Packets

Question: Discuss about the Time to Live field in IP packets and how this field is structured in both, IPv4 and IPv6 addressing schemes. Answer: Introduction Regardless of the IP packet, you consider (IPv4 or IPv6) they all have a familiar structure where an IP header is followed by a variable data field. Now, the header files will contain control information needed to deliver a packet from one end to another. Time to live (TTL) is an example of these files stored within the header files of an IP packet (Tutorial Point, 2017). Relevance of TTL As a header file, the time to live dictates the time taken by a data packet within a given network, therefore, it determines the overall lifetime of an IP packet within a network. This provision prevents data packets from having an extended lifetime especially during routing loops (Zander, Armitage Branch, 2007). Moreover, TTL determines the number of hops a certain packet will have before being discarded by a router. In itself this is another definition of TTL however, its able to give a deeper meaning of what the TTL does and its overall relevance. Consider this, a packet is a general and fundamental unit of transferring information in most networks today. On the other hand, a router is a network device (within the network layer), that connects two or more networks, for instance, two local area networks (LANs) or wide area networks (WANs). Finally, a hop is the overall distance or trip taken by a packet as it transverses from one router to another to get to its destination. Therefore, among its role, the TTL will assign the maximum hops (trips) to a packet before being dropped by a router (LINFO, 2005). In essence, the TTL value within a packet will tell a router whether it's been in the network for too long which facilitates the management of the network to minimise congestion and to account for all data packets. The TTL value is first set by the device or system sending the data packet (source). Its value can range from anywhere between 1 and 255 as dictated by the operating system. As the packet transverses the network, each router subtracts 1 from the existing value. Now, the packet is continuously passed on to the next router so long as the TTL value remains greater than 1. However, in case its 0, the packet is discarded and an Internet Control Message protocol is sent back to the source (Rouse, 2017). TTL in IPv4 As stated before, TTL is located within the header files and in IPv4 is usually the 9th octet having an 8-bit field size. In IPv4, the entire header file contains 20 octets as shown below. Version IHL Type of service Total Length Identification Flags Fragment Offset Time to Live Protocol Header Checksum Source IP address Destination IP address Options Padding TTL in IPv6 Similar to IPv4, the TTL field is usually located in the header files as the 8th field (octet) with an 8-bit size. Moreover, in IPv6 this value is known as the Hop Limit which clearly designates its role within the header files. Version Class Flow Control Payload Length Next Head Hop Limit Source Address Destination Address References Rouse. M. (2017). Time-to-live (TTL). Tech target. Retrieved 21 March, 2017, from: https://searchnetworking.techtarget.com/definition/time-to-live The Linux Information Project (LINFO). (2005). Time-to-live Definition. Retrieved 21 March, 2017, from: https://www.linfo.org/time-to-live.html Tutorial Point. (2017). IPv4 - Packet Structure. Retrieved 21 March, 2017, from: https://www.tutorialspoint.com/ipv4/ipv4_packet_structure.htm Zander. S, Armitage. G Branch. P. (2007). Dynamics of the IP Time to Live Field in Internet Traffic Flows. Centre for Advanced Internet Architectures. Retrieved 21 March, 2017, from: https://caia.swin.edu.au/reports/070529A/CAIA-TR-070529A.pdf