IP Datagram Header Fields 8 bits = 1 byte VER HLEN Diffentiated Services Total LEN Identification Flags Fragmentation offset TTL Protocol Header Checksum Source IP Address Destination IP Address Options DATA 4 bits 4 bits 8 bits 16 bits 16 bits 3 bits 13 bits 8 bits 8 bits 16 bits 32 bits 32 bits Version: Either IPv4 or IPv6 Total LEN: Total length of the datagram (IP header + data) Identification: Packet ID# used during segmentation and reassembly Flags: Used during segmentation and reassembly. Primarily used to indicate ?do not fragment? or ?there are more fragments coming?. Fragmentation Offset: Used during segmentation and reassembly to indicate the order for reassembly. Time to Live (TTL): Used to indicate the number of hops a packet can traverse before it is tossed. Number is decremented by one at each router hop. Protocol: Defines what type of data is encapsulated (ICMP, TCP, UDP, SCTP) Checksum: Calculated and entered by sender. Calculated and compared by receiver. If different, toss the packet ? it?s corrupt. Source IP address: IP address of the source (sender). It must remain unchanged as the packet traverses from SRC to DST. Destination IP address: IP address of the destination (receiver). It must remain unchanged as the packet traverses from SRC to DST. Amy Microsoft Word - IP Header.doc
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