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Lee Smet
53 lines
2.7 KiB
Markdown
53 lines
2.7 KiB
Markdown
# Data packet
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A `data packet` contains user specified data. This can be any data, as long as the sender and receiver
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both understand what it is, without further help. Intermediate hops, which route the data have sufficient
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information with the header to know where to forward the packet. In practice, the data will be encrypted
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to avoid eavesdropping by intermediate hops.
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## Packet header
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The packet header has a fixed size of 36 bytes, with the following layout:
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```
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Length | Reserved |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+ +
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+ Source IP +
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+ +
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+ +
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+ Destination IP +
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+ +
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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```
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The first 2 bytes are used to specify the length of the body. In practice, packets should be limited
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to at most the MTU size of the NIC used. This means that the leading bits should be unused. In the
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future, the protocol might be extended to take advantage of these unused bits.
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The next 2 bytes are reserved for future use and should be set to all 0.
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The next 16 bytes contain the sender IP address.
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The final 16 bytes contain the destination IP address.
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## Body
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Following the header is a variable length body. The protocol does not have any requirements for the
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body, and the only requirement imposed is that the body is as long as specified in the header length
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field. It is technically legal according to the protocol to transmit a data packet without a body,
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i.e. a body length of 0. This is useless however, as there will not be any data to interpret.
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