Objectives
Learn to create network packets.
Learn how packets can be sent over the network.
Familiarize you with the concept of sockets.
Learn packing structures, endianness, unpacking, and interpreting network data.
Learn how to use actual data from a packet.
Use packet capture to visually inspect protocols.
Overview
HINT: Look at python “argparse” module for this portion.
$ lightserver -p <PORT> -l <LOG FILE LOCATION>
1.PORT - The port server listens on.
2.Log file location - Where you will keep a record of actions.
For example:
$ lightserver -p 30000 -l /tmp/logfile
Deliverables (each worth 5 points)
Write a server that listens for incoming connections on the specified port.
Server must parse two command line arguments, port and log locations.
The server must not exit after receiving a single packet.
Once a client connects, it logs a message in the following format "Received connection from <CLIENT IP, PORT> "
Once it receives a HELLO message from the client, it logs the connection and sends a HELLO back to the client.
You can assume the packet format is the following:
+-----------------+--------------------------+-------------------------+
| | | |
| | | |
|Version(4 bytes) |Message type (4 bytes) |Message Length (4 bytes) |
| | | |
| | | |
+-----------------+--------------------------+-------------------------+
| |
| |
| Message (Max 10 Bytes) |
| |
| |
+----------------------------------------------------------------------+
It receives the packet header first, followed by the message. Hint: You need two RECV calls.
Check if Version == 17. If not, log an error message VERSION MISMATCH and continue to listen. Do not exit.
If Version == 17, check the message type. If message Type is 1 - the corresponding command is LIGHTON. If message type is 2 - the corresponding command is LIGHTOFF. No other command is supported.
If the server sees a supported command, log “EXECUTING SUPPORTED COMMAND: COMMANDNAME”, else log <“IGNORING UNKNOWN COMMAND: COMMANDNAME”.
Send back a “SUCCESS” message to the client.
Make sure server does not exit on 0 byte messages.
On receiving a DISCONNECT message from the client, it closes that particular socket. The whole program should not exit.
Server can handle multiple clients at a given time.
Client Specifications
$ lightclient -s <SERVER-IP> -p <PORT> -l LOGFILE
The client takes three arguments:
1.Server IP - The IP address of the server.
2.PORT - The port the server listens on.
3.Log file location - Where you will keep a record of packets you received.
For example:
$ lightclient -s 192.168.2.1 -p 6543 -l LOGFILE
The client must parse three command line arguments, server, port, and logfile.
The client should connect to the server on the specified port.
Constructs and sends a hello packet to the server.
+-----------------+--------------------------+-------------------------+
| | | |
| | | |
|Version(4 bytes) |Message type (4 bytes) |Message Length (4 bytes) |
| | | |
| | | |
+-----------------+--------------------------+-------------------------+
| |
| |
| Message (HELLO) |
| |
| |
+----------------------------------------------------------------------+
Receive reply from Server - if version is 17, log “VERSION ACCEPTED”, else log - “VERSION MISMATCH”
If version is accepted, send a command packet.
+-----------------+--------------------------+-------------------------+
| | | |
| | | |
|Version(4 bytes) |Message type (4 bytes) |Message Length (4 bytes) |
| | | |
| | | |
+-----------------+--------------------------+-------------------------+
| |
| |
| COMMAND (LIGHTON/LIGHTOFF) |
| |
| |
+----------------------------------------------------------------------+
Receive the server’s reply, log the reply, send a DISCONNECT message to the server, and shutdown the socket. You can assume the server always replies with a “SUCCESS” message for this assignment.
Use TCPDUMP or Wireshark to capture the interactions, turn the .pcap file in with the assignment.
Break the problem down in smaller portions - don’t try to do everything at once.
Use ARGPARSE module for parsing the command-line arguments.
Code must compile/run on Google Cloud Ubuntu VM (18.04 or later).
You must pack the packet in a structure. If you are using python, use the “STRUCT” module. See an example here: https://pymotw.com/3/struct/
Pay extra attention to byte-order encoding before sending the packet. Big-endianness is the dominant ordering in today’s network protocols.
Server side
Received connection from (IP, PORT): ('127.0.0.1', 53888)
Received Data: version: 17 message_type: 1 length: 1280
VERSION ACCEPTED
EXECUTING SUPPORTED COMMAND: LIGHTON
Returning SUCCESS
Received connection from (IP, PORT): ('127.0.0.1', 53890)
Received Data: version: 17 message_type: 2 length: 1792
VERSION ACCEPTED
EXECUTING SUPPORTED COMMAND: LIGHTOFF
Returning SUCCESS
Client Side
Run 1
Received Data: version: 17 type: 1 length: 1280
VERSION ACCEPTED
Received Message Hello
Sending command
Received Data: version: 17 type: 2 length: 1792
VERSION ACCEPTED
Received Message SUCCESS
Command Successful
Closing socket
Run 2
Sending HELLO Packet
Received Data: version: 17 type: 1 length: 1280
VERSION ACCEPTED
Received Message Hello
Sending command
Received Data: version: 17 type: 2 length: 1792
VERSION ACCEPTED
Received Message SUCCESS
Command Successful
Closing socket
