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Ethernet messagging using raw-sockets in Linux

Description

Ethernet cache (EC) - very basic, for education purposes, implementation of message caching Server and Client that work over Ethernet using raw-sockets in Linux. Client sends a request with a command and a message with an ID from 0 to 127, and the server stores or returns a message depending on the command: save or, respectively, retrieve it.

Build

make

Usage

Client:

Usage:
        client SRC_NIC MAC_DST 0-127 'Message to send'
        client SRC_NIC MAC_DST 0-127

For example, to send:
        client enp0s3 22:22:22:22:22:22 34 'foo bar baz bam'
And to retrieve:
        client enp0s3 22:22:22:22:22:22 56

Server:

Usage:
        server NIC

Example:
        server enp0s3

Implementation notes

  • EC uses 802.3, also known as historical Novell raw, frames. Using this non-common frame type allows to cut off Ethernet II noise on the network interfaces without need of MAC address filtering

  • Fixed-size frames are always used, that limits effective message length to a maximum of 1493 bytes. Zero padding is applied for shorter messages. The same technique refers to the message buffer on the server

  • On retrieve command, server always replies with a message. If the message is empty, e.g. ID has never been used before, the message contains only padding

  • If client sends only padding with the save command, the server "clears" the slot with the specified ID

  • For the sake of simplicity, as there is just a small number of IDs possible (0-127), the server maintains a fixed size array of strings to save messages, where ID of a message is an element index of the array

  • Written on Ubuntu 24.04.1 LTS

Format of the frame payload

  • 1-st byte:
    • 1 bit command; 0 - save message; 1 - retrieve message
    • 7 bits message ID;
  • 2-1493 bytes:
    • Zero-padded message

Contacts

I would appreciate any feedback, additions, fixes and suggestions, sincerely yours Mikhail Zakharov zmey20000@yahoo.com