I am trying to send commands to a server via a python script. I can see the socket connection being established on the server. But the commands I am sending across , do not seem to make it through(server does a read on the socket).
The server currently supports a telnet command interpreter. ie: you telnet to the command address and port, and you can start sending
string commands.
My question is , is there anything fundamentally different from sending strings over a tcp socket, as opposed to using telnet.
I have used both raw sockets as well as the Twisted framework.
Telnet is a way of passing control information about the communication channel. It defines line-buffering, character echo, etc, and is done through a series of will/wont/do/dont messages when the connection starts (and, on rare occasions, during the session).
That's probably not what your server documentation means. Instead, it probably means that you can open a TCP socket to the port using a program like "Telnet" and interact with a command interpreter on the server.
When the Telnet program connects, it typically listens for these control messages before responding in kind and so will work with TCP/socket connections that don't actually use the telnet protocol, reverting to a simple raw pipe. The server must do all character echo, line buffering, etc.
So in your case, the server is likely using a raw TCP stream with no telnet escape sequences and thus there is no difference.
Keep in mind that Telnet is an application layer protocol while TCP is a transport layer protocol. Telnet uses TCP in order to transmit data. That is a big fundamental difference between Telnet and TCP.
See: OSI Model wikipedia page
From the Wikipedia page on telnet
...User data is interspersed in-band with Telnet control information...
So, to answer your question, yes, telnet does differ from a raw socket.
RFC 854 describes the telnet protocol if you want to try implementing it or you could use telnetlib if you'd prefer an existing python client.
Related
The title pretty much describes the question: if I send a packet containing, I don't know, some text inside it, from a python program to an other, if there's a hacker sniffing packets on the network, would they be able to see the content of the packet?
If you use a plain TCP or UDP socket then the data you write into this socket are transferred in clear on the wire and can be sniffed unless the OS employs encryption at the network layer or lower layers, i.e. VPN technologies like IPSec, OpenVPN or similar.
If instead you are using an SSL wrapped socket then the data will be encrypted inside the application and thus protected against sniffing provided that the SSL socket was created with secure settings (strong ciphers, proper certificate validation).
I am creating a colloabrative note-making app in python.
Here, one guy on computer running the app can create the server subseuqently the changes on the screen([color, pixel], where pixel=[x,y]) will be transmitted to others connected to the server.
I am using kivy for creating the app. My question is with respect to transmitting the data over the server.
I can create server using this:
import socket
ip_address=socket.gethostbyname(socket.gethostname())
execfile( "manage.py runserver "+ip_address+":8000" )
Now, how do others connect to the server and request the data(assuming the above code is correct). Also, how to send the data in django.
Well, Django is a framework that allows creating a site or API that is reachable through HTTP protocol. This has several consequences for you:
Server cannot send a message to client unless the client asks. HTTP is a "request-response" protocol. Client sends a request (for example, http://server.com/getUpdates?id=100500) and gets a response from server.
Creating clients that ask the server to give them updates all the time is a bad practice, probably leading to server DoS.
Although you can use WebSockets, using Django for such a task is really an overkill.
Summarizing, you need a reliable duplex channel for sending data in both directions. I'd start with TCP server, rather than HTTP. Fortunately, Python stdlib has a module you can start with - socketserver.
Additional reading
TCP
UDP (you will probably want this for broadcasting)
Berkeley sockets (a socket standard underlying socketserver module)
TCP vs. UDP
When deciding what protocol to use, following aspects should be considered:
TCP is reliable. Messages never disappear implicitly. If there was a network error, message will be resent. If there's no connection, explicit error will be raised. TCP uses several algorithms to fit into the network channel. It is an intelligent protocol.
UDP is unreliable. It possesses no feature TCP has. Packets can disappear, get reordered. But UDP messages are lightweight and in experienced hands they summon to life such systems as network action games and streaming video (lost and reordered messages aren't crucial here and TCP becomes too slow).
So I'd recommend to start with TCP. It's way more easier to get working fast and correct than UDP. Switch to UDP if you have some experience with TCP and there are a lot of people using you app and wanting to get the lowest latency possible.
Using a Lantronix UDS-1100 serial to IP converter. The goal is to write a small proof of concept piece in Python to capture serial data output by this device over IP.
I've done a couple test projects using sockets in python, but they were all done between python processes (python > python): listen() on one end, and connect(), sendall() etc on the other.
I think I can use sockets for this project, but before I invest a bunch of time into it, wanted to make sure it is a viable solution.
Can python sockets be used to capture IP traffic when the traffic is originating from a non-python source? I have full control over the IP and port that the device sends the serial data to, but there will be no python connect() initiated by the client. I can pre-pend then serial data with some connect() string if needed.
If sockets won't work, please recommend another solution...guessing it will be REST or similar.
Of course. TCP/IP is supposed to be cross-platform and cross-language, so in theory you should be able to communicate with every kind of device as long as you manage to process and send the expected protocol.
We occasionally have to debug glitchy Cisco routers that don't handle the TCP Selective Acknowledgment (SACK) options correctly. This causes our TCP sessions to die when routed through an IPTABLES port redirection rule.
To help with the diagnosis, I've been constructing a python-based utility to construct a sequence of packets that can reproduce this error at will, the implementation uses raw sockets to perform this trick. I've got an ICMP ping working nicely but I've run into a snag on the UDP implementation, I can construct, send and receive the packet without problem, the issue that I'm seeing is that Linux doesn't like the UDP packets being sent back from the remote system and always sends an ICMP Destination unreachable packet, even though my python script is able to receive and process the packet without any apparent problems.
My question: Is it possible to subsume the Linux UDP stack to bypass these ICMP error messages when working with RAW sockets?.
Thanks
Are you receiving and processing the packet and only need to suppress the ICMP port-unreachable? If so, maybe just add an entry to the iptables OUTPUT chain to drop it?
Is there any way to send ARP packet on Windows without the use of another library such as winpcap?
I have heard that Windows XP SP2 blocks raw ethernet sockets, but I have also heard that raw sockets are only blocked for administrators. Any clarification here?
There is no way to do that in the general case without the use of an external library.
If there are no requirements on what the packet should contain (i.e., if any ARP packet will do) then you can obviously send an ARP request if you're on an Ethernet network simply by trying to send something to any IP on your own subnet (ensuring beforehand that the destination IP is not in the ARP cache by running an external arp -d tar.get.ip.address command), but this will probably not be what you want.
For more information about raw socket support see the TCP/IP Raw Sockets Docs page, specifically the Limitations on Raw Sockets section.
You could use the OpenVPN tap to send arbitrary packets as if you where using raw sockets.