I need some data which was stored in a scale machine [machine have some ip address (http:122.168.1.12:30)]. i want to How to establish a TCP connection from a web browser to machine (client side) . here i want to connect machine with tcp/ip address, read and display that data in browser with click event. can any one please let me know how to do this using node js or javascript. in web browser
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I've connected two devices to the same personal hotspot (e.g. using an iPhone's one). I did it because I want to create a local network where the two devices can communicate with each other and also both can access to the Internet.
One is the Client, the other one plays the role of the Server and hosts a website. The two devices can ping each other but when I open the browser on the Client and put the Server's IP address and the port where the website is served, for example 172.20.10.8:3000, nothing gets displayed and eventually the page shows the request has run out of time.
This issue happens also when using an Android device's hotspot. On the other hand, when I connect both to a normal Wifi network everything works just fine.
Does it mean there's some sort of limitations when using a Hotspot?
Eventually I've found out that you need to set the Hotspot connection as a Private Network in both clients. Otherwise it will be set to Public Network and the devices' IP Address would not be visible by others.
I am using my device as an Access Point and I need to display a deafault web page once somebody is connected.
Right now I have to connect to a specific IP (socket parameters: IP 192.168.0.1 , PORT 80) to show the page.
The page doesn't need to open automatically, it just has to show up no matter what URL gets inserted in the browser.
I've read the RFC7710 but I'm not able to implement "low level" solutions such as modify the option 160 of the DHCP.
The best thing for me would be to work at the HTTP level.
Any ideas?
HTTP works on the top of the TCP/IP infrastructure, it requires an established TCP connection first. As long as there is no TCP connection from the client to the HTTP server, the server has no way to tell, force, or trick a client to connect to its IP address and TCP port. No connection, no HTTP.
Our project is LIDAR which is based on physics. The total equipment is connected to server which consists of various sensors. Server gives total information about the equipment like temperature, humidity etc. Server and laptop are connected through LAN. Our work is to develop a software using labview which interfaces the equipment with the laptop. To achieve that first we have to connect the server to the laptop. We have tried in so many ways using TCP/IP vi in labview. Both server and client programs are required to do this. In the server program we are using TCP Listen and in the client program we are using TCP open connection. Which IP address and port address should be given to TCP listen and TCP open coonection ?
The IP address and port should refer to the server as shown in this snippet (replace port with your chosen port and localhost with your server address):
The example code I have shown above has two code blocks, the TCP Server should run on your server and the TCP Client should run on your laptop. The remote address would then need to be changed to the address of your server. Using the above example only shows how the connection is made and a single item of data transferred before closing the connection. You would need to wrap up some extra code to provide any handshaking between the server and laptop to provide the required functionality in your application.
In LabVIEW you will find some examples on how to use the TCP function, from the top menu select 'Help' and 'Find Examples...' then using the 'Search' tab type in TCP and you will see 'Simple TCP.lvproj' that should give you something that will get you going.
If your project doesn't specifically require you to use the TCP listen/open VIs then you might want to consider some of the built in networking functionality that comes with LabVIEW.
I've had good luck with LabVIEW's network shared variables stuff where you can, among other things, connect a front panel control on the client to a variable shared by the server, and LabVIEW takes care of all of the TCP functions behind the scenes.
Here's one webpage about the feature:
http://zone.ni.com/reference/en-XX/help/371361G-01/lvconcepts/ni_psp/
I am new to network programming and try to understand managing traffic via TUN/TAP interface.
Since I have almost nonexistent system programming skills, and feel confident on Java; I use OpenVPN tun/tap driver and ready made Java binding for it. It works on TAP mode.
As an example application I am trying to imitiate no encryption, no authentication client server VPN application.
I can catch Ethernet Frame packets, but for the routing part, I failed miserably. (I can modify route/arp tables.)
Do anybody know how OpenVPN send packets from client to server, and from server to target. Opening sockets from Java looks like an alternative; but I was hoping that modifying packets(change IPs and/or MAC addresses) and writing back to the virtual tap interface would be enough. Is it so?
Can I inject packets to send other locations, or by default received packet moves towards application layer?
-- Edit:
Scneario
Client Tap0 _____ Server Tap0 ______ Target
Eth0 Eth0
Target: Ping from client, move through tap interfaces, target see only server ip (anonymization)
What I achived so far.
Catch traffic at client tap0 interface.
I coulnt forward traffic at server Tap so to fasten things I used Java socket programming between client-server.
Now I read packets from socket at server, and try to OpenVPN Tap driver's write method to move forward but I am not sure where do I fail. I see packets with tcpdump at server tap0, but they do not pass to server eth0.
My most important question is if I modify packet(ip, mac address) and call write method, is it possible that packet moves forward. (Or does it move to application layer whatever you change??)
Any help would be appreciated.
1. Routing is a Layer 3 (IP) problem and handled by the OS. As for the Ethernet frames on Layer 2, you have multiple options. In any case, you'll have to parse the incoming packets' headers and extract the MAC address, and decide based on the MAC where to pass the packet: To a specific client, all clients (broadcasts) or the local tap interface.
Option 1: On each client, use a tun device, and let the server use a tap device. Assign pseudo MAC addresses to each client, respond accordingly to ARP requests from the server's OS and let the OS on the server take care of the rest. Applicationwise, you'll only have to forward all incoming packets to the tap device and all outgoing packets to the client to which you assigned this MAC.
Option 2: Let the clients choose their own MAC address and forward ARP-requests through the network. The server application has to decide for incoming packets from a client whether to forward the packet to a client, or send it to the local tap device if the address matches the local device's MAC.
In both cases, clients pass all packets from their local tun/tap device to the server and vice versa.
2. You can do almost anything. A packet is only "received" when you decide to write it to the tap device, and you can of course temper with any packets, or inject new ones, ...
As a final comment, I've found that toying with tun devices is conceptually simpler, because they work on Layer 3. You'll have to open a tun device on the server for each client, but within your application you'll have to do nothing but to forward anything coming from the device to the single client, and vice versa.
Can someone tell me what is the difference between active and passive FTP?
Which one is preferable?
Active and passive are the two modes that FTP can run in.
For background, FTP actually uses two channels between client and server, the command and data channels, which are actually separate TCP connections.
The command channel is for commands and responses while the data channel is for actually transferring files.
This separation of command information and data into separate channels a nifty way of being able to send commands to the server without having to wait for the current data transfer to finish. As per the RFC, this is only mandated for a subset of commands, such as quitting, aborting the current transfer, and getting the status.
In active mode, the client establishes the command channel but the server is responsible for establishing the data channel. This can actually be a problem if, for example, the client machine is protected by firewalls and will not allow unauthorised session requests from external parties.
In passive mode, the client establishes both channels. We already know it establishes the command channel in active mode and it does the same here.
However, it then requests the server (on the command channel) to start listening on a port (at the servers discretion) rather than trying to establish a connection back to the client.
As part of this, the server also returns to the client the port number it has selected to listen on, so that the client knows how to connect to it.
Once the client knows that, it can then successfully create the data channel and continue.
More details are available in the RFC: https://www.ietf.org/rfc/rfc959.txt
I recently run into this question in my work place so I think I should say something more here. I will use image to explain how the FTP works as an additional source for previous answer.
Active mode:
Passive mode:
In an active mode configuration, the server will attempt to connect to a random client-side port. So chances are, that port wouldn't be one of those predefined ports. As a result, an attempt to connect to it will be blocked by the firewall and no connection will be established.
A passive configuration will not have this problem since the client will be the one initiating the connection. Of course, it's possible for the server side to have a firewall too. However, since the server is expected to receive a greater number of connection requests compared to a client, then it would be but logical for the server admin to adapt to the situation and open up a selection of ports to satisfy passive mode configurations.
So it would be best for you to configure server to support passive mode FTP. However, passive mode would make your system vulnerable to attacks because clients are supposed to connect to random server ports. Thus, to support this mode, not only should your server have to have multiple ports available, your firewall should also allow connections to all those ports to pass through!
To mitigate the risks, a good solution would be to specify a range of ports on your server and then to allow only that range of ports on your firewall.
For more information, please read the official document.
Redacted version of my article FTP Connection Modes (Active vs. Passive):
FTP connection mode (active or passive), determines how a data connection is established. In both cases, a client creates a TCP control connection to an FTP server command port 21. This is a standard outgoing connection, as with any other file transfer protocol (SFTP, SCP, WebDAV) or any other TCP client application (e.g. web browser). So, usually there are no problems when opening the control connection.
Where FTP protocol is more complicated comparing to the other file transfer protocols are file transfers. While the other protocols use the same connection for both session control and file (data) transfers, the FTP protocol uses a separate connection for the file transfers and directory listings.
In the active mode, the client starts listening on a random port for incoming data connections from the server (the client sends the FTP command PORT to inform the server on which port it is listening). Nowadays, it is typical that the client is behind a firewall (e.g. built-in Windows firewall) or NAT router (e.g. ADSL modem), unable to accept incoming TCP connections.
For this reason the passive mode was introduced and is mostly used nowadays. Using the passive mode is preferable because most of the complex configuration is done only once on the server side, by experienced administrator, rather than individually on a client side, by (possibly) inexperienced users.
In the passive mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server, which the client then uses to open a data connection to the server IP address and server port number received.
Network Configuration for Passive Mode
With the passive mode, most of the configuration burden is on the server side. The server administrator should setup the server as described below.
The firewall and NAT on the FTP server side have to be configured not only to allow/route the incoming connections on FTP port 21 but also a range of ports for the incoming data connections. Typically, the FTP server software has a configuration option to setup a range of the ports, the server will use. And the same range has to be opened/routed on the firewall/NAT.
When the FTP server is behind a NAT, it needs to know it's external IP address, so it can provide it to the client in a response to PASV command.
Network Configuration for Active Mode
With the active mode, most of the configuration burden is on the client side.
The firewall (e.g. Windows firewall) and NAT (e.g. ADSL modem routing rules) on the client side have to be configured to allow/route a range of ports for the incoming data connections. To open the ports in Windows, go to Control Panel > System and Security > Windows Firewall > Advanced Settings > Inbound Rules > New Rule. For routing the ports on the NAT (if any), refer to its documentation.
When there's NAT in your network, the FTP client needs to know its external IP address that the WinSCP needs to provide to the FTP server using PORT command. So that the server can correctly connect back to the client to open the data connection. Some FTP clients are capable of autodetecting the external IP address, some have to be manually configured.
Smart Firewalls/NATs
Some firewalls/NATs try to automatically open/close data ports by inspecting FTP control connection and/or translate the data connection IP addresses in control connection traffic.
With such a firewall/NAT, the above configuration is not necessary for a plain unencrypted FTP. But this cannot work with FTPS, as the control connection traffic is encrypted and the firewall/NAT cannot inspect nor modify it.
Active mode:
-server initiates the connection.
Passive mode:
-client initiates the connection.
Active Mode—The client issues a PORT command to the server signaling that it will “actively” provide an IP and port number to open the Data Connection back to the client.
Passive Mode—The client issues a PASV command to indicate that it will wait “passively” for the server to supply an IP and port number, after which the client will create a Data Connection to the server.
There are lots of good answers above, but this blog post includes some helpful graphics and gives a pretty solid explanation: https://titanftp.com/2018/08/23/what-is-the-difference-between-active-and-passive-ftp/