Diff for "InternetProtocolV4"

IPv4 Protocol Notes

http://www.scotnpatti.com/unl/images/ipv4.jpg

Version

Only 4 bits, this field determines the how the rest of the packet is treated

Default Value: None

HLen

HLen is the header length and is specified as the number of 32 bit words. Thus the header is at most 480 bits (2^4 - 1) * 32.

Default Value: 5, because we don't specify any options varibles.

TOS

This field has had a number of different definitions over the years and is generally used to define the values used on routers etc.

Default Value: None

Length

This field gives the length of the entire datagram in bytes rather than words. Thus the maximum length of a IP datagram is 65535

NOTE: THE NEXT WORD DEAL WITH FRAGMENTATION

Ident

Flags

Offset

TTL

The intent is to limit the time (in seconds) a packet can wander around an internet in loops before it is discarded. Since most routers do not synchronize their clocks, each router just decrements the value by one and discards it when it gets to 0.

Default Value: 64

Protocol

This field defines a multiplexing key that determines which higher level protocol to pass the data to. On Linux systems see /etc/protocols. TCP = 6, UDP = 17.

Checksum

The checksum is calculated by considering the entire IP header as a sequence of 16-bit words added using one's complement arithmetic, and taking the ones complemnt result. The checksum is calculated using the IpCheckSum algorithm. This is not as good as CRC, but it's faster and easier to implement.

SourceAddr

DestinationAddr

Options(Variable)

Pad (Variable)

Data