38 lines
1.2 KiB
Markdown
38 lines
1.2 KiB
Markdown
# Internet protocol Version 4 (IPV4)
|
|
|
|
- IP is the principal communications protocol in the network layer.
|
|
- IP has the task of delivering packets from source host to destination host based on IP addresses.
|
|
|
|
IP defines datagram structure that encapsulate the data to be delivered.
|
|
|
|
An IP datagram (packet) consists of a header part an a text part. (payload)
|
|
|
|
The header has a 20 byte fixed part an a variable length optional part.
|
|
|
|
![[IP-packet.png]]
|
|
|
|
Some of the fields in a packet are not always used.
|
|
|
|
## Packet encapsulation
|
|
Packets are encapsulated in data link frames (Ethernet)
|
|
|
|
![[packet-enscapsulation-2.png]]
|
|
|
|
## Fragmentation
|
|
Mostly, data link frames are smaller in size than IP Packets
|
|
So the IP Packet does not fit in the data link frame.
|
|
|
|
In these cases the packet is split up into multiple parts (fragments) and each fragment is send in a separate frame.
|
|
|
|
![[packet-fragmentation.png]]
|
|
|
|
The receiver host then combines all fragments before using them
|
|
|
|
Therefore the receiver should know which part of the message each fragment belongs (hence the fragment offset field in IP header)
|
|
|
|
![[packet-fragmentation-2.png]]
|
|
|
|
Ecapsulating a packet in a frame requires:
|
|
|
|
- Sender MAC Address (can be found out)
|
|
- Receiver MAC Address (Should be found out |