Telematics Chapter 6: Network Layer - Freie Universität Berlin

The IP Header (2)
● DF (1 bit): Don't Fragment. All routers must forward packets up to a size of 576
byte, everything beyond that is optional. Larger packets with set DF-bit therefore
cannot take each possible way in the network.
● MF (1 bit): More Fragments
● “1” - further fragments follow
● “0” - last fragment of a datagram
● Fragment Offset (13 bits): Sequence number of the fragments of a packet (2 13
= 8192 possible fragments). The offset states, to which position of a packet
(counted in multiples of 8 byte) a fragment belongs to. From this a maximum
length of 8192 x 8 byte = 65,536 byte results for a packet.
● Protocol (8 bits): Which transport protocol is used in the data part (UDP,
Type of
TCP,…)? To which transport process the packet has Version to IHL be passed? Service
Total Length
D M
Identification Fragment Offset
● Header Checksum (16 bits): 1’s complement of the sum of the 16-bit F F half
words of the header. Must be computed with each hop (since Protocol TTL changes)
Time to Live Header Checksum
Source Address
● Source Address/Destination Address (32 bits): Network and host numbers
Destination Address
of sending and receiving computer. This information is used by routers for the
routing decision.
Options (variable, 0-40 Byte)
Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 6: Network Layer
DATA (variable)
Padding
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