AN2120: Connecting an M68HC08 Family Microcontroller to an ...

Application Note
Version
A brief description of each of the fields found in an IP packet is given in
Table 1.
Table 1. Fields in an IP Packet
Field Description
Indicates the format of the Internet header. Two values are valid for this field: Four
(current IP standard) and six for the future IPv6.
IHL (IP header length) The length of the Internet header measured in 32-bit words, usually 5
Type of service Specify reliability, precedence, delay and throughput parameters
Total Length Total length of the datagram (header and data) measured in bytes
Identification An ID assigned by the sender to aid in assembling fragmented datagrams
Flags (3 bits)
One bit indicates fragmentation; another is the "Don't fragment" bit, specifying whether
the fragment may be fragmented. The last bit is reserved.
Fragment offset Indicates a fragment portion
Time to live Indicates the maximum time the datagram is allowed to remain in the Internet
Protocol Indicates the next layer protocol which is to receive the payload of the datagram
Header checksum A checksum of the header only
Source address The sender IP address
Destination address The destination IP address
Options
The option field is variable in length and is optional. There may be zero or more
options. This application note does not support options.
Padding If options are present, padding ensures the IP header ends on a 32-bit boundary.
Data Payload of the datagram
An example of an IP datagram is shown in Figure 7. Notice how the IP
packet carries ICMP data of a ping request from 192.168.55.2 to
192.168.55.1.
45 00 00 1C 00 F4 00 00 80 01
A4 99 C0 A8 37 02 C0 A8 37 01
08 00 F6 51 01 00 00 AE
Figure 7. Example of an IP Datagram with ICMP Payload
AN2120
10 MOTOROLA