ptimization. The Total Length field indicates the length (in octets) of the entire packet, including both the header and the data within the packet. The maximum size of an IP packet is 64 KB (OK, 65,535 bytes). When a packet is broken into smaller "chunks" (a process called frag- mentation) during transmission, the Identification field is used by the transmitting host to ensure that all of the fragments from a single mes- sage can be reassociated at the receiving end, to ensure message reassembly. The Flags also play a role in fragmentation and reassembly. The first bit is referred to as the More Fragments (MF) bit and is used to indicate to the receiving host that the last fragment of a packet has been received, SO that the receiver can reassemble the packet. The second bit is the Don't Fragment (DF) bit, which prevents packet fragmentation (for delay sensitive applications, for example). The third bit is unused and is always set to 0. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Transport Technologies The Fragment Offset field indicates the relative position of this par- ticular fragment in the original packet that was broken up for transmis- sion. The first packet of a fragmented message will carry an offset value of 0, while subsequent fragments will indicate the offset in multiples of 8 bytes. Makes sense, no? I love this field. A message is fragmented into a stream of packets and the packets are all sent on their merry way to the destination system. Somewhere along the way packet number 11 decides to take a detour and ends up in a routing loop on the far side of the world, trying in vain to reach its destination. To prevent this packet from living forever on the Internet, IP includes a Time-to-Live (TTL) field. This configurable field has a value between 0 and 255 and indicates the maximum number of hops that 