Have you seen those apps which explore your local network looking for devices?
Well, I would like to know how they get (mostly) the names of devices!
Does anyone know? Because I am building an application which needs to get (if possible) the hostname of the local devices..
Local network device discovery is often done by a zeroconf implementation (e.g. Apple services typically use Bonjour services to discover local device names).
If you wanted to explore this type of service for use in nodeJS, then maybe have a look at https://github.com/agnat/node_mdns. I've never used it myself but it does seem reasonably popular and stable.
Otherwise just do some research generally around zeroconf/mdns and make a decision based on your needs.
Related
I need a way for my application to find someone with the same application on a local network.
But can't find the docs to use a protocol like SSPD. It says its UDP on port 1900 and the ip 239.255.255.250.
It also says it can use NOTIFY and M-SEARCH.
But that is it. I've hit a wall. And I need some guidence.
OVERVIEW
Trying to make my apps automatically find each other and exchange ip/names on a local network so they can talk to each other p2p-style without a connection broker.
The UPnP Device Architecture reference contains the de-facto SSDP reference: it's very similar to the IETF spec and has dozens of well tested implementations already. Chapter 1 contains everything needed to implement SSDP, assuming you know how to send and receive multicast and unicast UDP messages.
My advice on implementing SSDP: Don't. It may look simple but there are a lot of gotchas on the way. Find a library or service that does SSDP for you. If you are on linux I suggest GSSDP (reference, code) (but I'm a bit biased having worked on it). I would assume other platforms have similar libraries.
I want to code a simpe vpn as a part of my course work. I am looking for ways to start. Will be helpful if you guys could help me with resources
As a basic starting point, you need to be able to write a client/server setup in your language of choice that will transport over IP. Your VPN must also be able to present the operating system with a network interface. If you are using Linux, I suggest the tun/tap system interface. For reference, you could look at the code in qemu which does make use of those OS calls. For the encryption purposes, the OpenSSL library should be able to provide you with all the calls necessary.
I'm not sure what the ultimate requirements of your coursework are. You can build anything from a basic shared-symmetric key setup that can be quickly hacked up to the bottomless pit of trying to build a production worthy VPN system. You should mention your requirements.
i am newbie to Linux platform, i am working on java technology.
what i have to do is : Having a program that running on mobile devices,that sends some data to my Linux machine, now i have to create a program in java that
listen to a particular port.
access data comes on that port(which is sending by mobile device)
save that data to the database.
response back to the mobile device.
i.e. i would make my Linux system as server that can listen from many clients(mobile devices), but not getting how to configure this environment... :(
i used cent OS 5.4 and
installed jdk1.6.0_24
any help would be appreciated.....
thanx in advance!
khushi
One of Java's greatest strengths is that you can pretty much ignore the host operating system as long as you stick to core Java features. In the case you're describing, you should be able to accomplish everything by simply using the standard Java networking APIs and either the JDBC to access an existing, external database or you could choose any number of embedded Java databases such as Derby. For your stated use case, that you'll be running the application on Linux is pretty much irrelevant (which should be good news... you don't need to learn a whole operating system in addition to writing your app ;-).
Here's a nice client/server tutorial, in that it is broken into steps, and adds each new concept in another step.
Here's another client/server tutorial with much more detail.
I would write it to accept one connection at a time. Once that works, I would study the new(ish) java.lang.concurrent classes, in particular the ExecutorService, as a way of managing the worker bee handling each connection. Then change your program to handle multiple connections using those classes. Breaking it up in two steps like that will be a lot easier.
I have tried using several commands as well as couple of examples using C/C++ but am still not able to find a flawless method that can differentiate between physical or virtual ethernet adapters. Physical means, on that available on your board or installed externally and virtual means created by virtualization apps such as VirtualBox/VMWare/Virtual PC or VPN etc.
Any pointers?
There is no flawless method. A virtual adapter can have any MAC address, including one that might have been assigned by a constructor to a physical device. And the other way around, given that one can change the MAC address of a physical adapter. You can only make an educated guess.
You might find it easier to detect if you are running virtualized at all, rather than look for specific information about the NICs. The virt-what(1) tool looks through aspects of the running system to guess if the system is virtualized or not. (The script isn't as smart as you think, but it does have a lot of small information gathering tools in one place.)
Someone intentionally trying to bypass a license check would probably not find it difficult to defeat this mechanism.
Maybe one can use mii-tool and check if it fails, which it does for virtual:
mii-tool vmbr2
SIOCGMIIPHY on 'vmbr2' failed: Operation not supported
mii-tool eno1
eno1: negotiated 1000baseT-FD flow-control, link ok
EDIT:
What is mii-tool: view, manipulate media-independent interface status
This utility checks or sets the status of a network interface's
Media Independent Interface (MII) unit. Most fast ethernet
adapters use an MII to autonegotiate link speed and duplex
setting.
https://www.man7.org/linux/man-pages/man8/mii-tool.8.html
Need a basic direction in the following project.
There is a linux based controller doing some industrial control stuff.
The box is equipped with cellular modem and is capable to get online through cellular carrier. Cellular communication is used because controller is mostly installed where no cables or short range radio is available. Places where sun don't normally shine :)
The task is to allow internet clients to connect directly to the box for some basic control/monitoring stuff. The problem is connectivity - how clients will discover the box? - I'd like to have the box act as a server (if possible). Assuming that cellular carrier allows the box to get online doesn't necessarily mean that the box will get public IP so that anyone would be able to get connected. To my understanding the cellular network acts as a gateway from those who are working inside of it, and reaching someone in that network from outside isn't possible. Am I wrong? We are looking for a generic solution, not a solution around particular cellular provider. The controller is installed in different countries, we need to find the standard way to "webify" it.
The software (and hardware) in the box is ours, we can basically do anything, but I am looking for the right way to do it in order to avoid surprises with different providers later. BTW, the solution doesn't necessarily have to be technical, may be it's possible to buy a permanent IP's per box, or setup VPNs.. Which way should I dig to? What questions to ask?
Your ideas are welcome!
Your summary of the problem is basically correct. I've implemented several systems that do this, and the odds of success are good.
The way you tackle this will depend on the number of remote units you expect a single user to interact with. If each user will handle only one or two devices, it's plausible to implement the web server on the remote device. If each user handles many devices, consider centralising as much administration as possible. I've implemented this using Zenoss for data logging, and a custom control server.
If the web server sits on the remote device, you can either buy a SIM with a static IP, or use a proxy server. I recommend setting up a proxy server unless the number of devices is very small.
There are three options for SIMs:
Static IP with an address on the public Internet will be expensive, and negotiating the deal with each provider in each country will be irksome. No proxy server is required.
Private APN SIMs will give you the option of a static address, but in a private address range. Negotiation with the mobile network is still required, and you will require a proxy server to sit between the public Internet and the private address range,
Standard data SIMs will connect to the Internet through NAT. You can use these to host your service by opening a VPN connection (we used openvpn) to your server. You can now reach the devices directly by connecting to the same VPN, or through a proxy server.
If you use openvpn, here are some more tips:
Give each unit a public serial number, and a private key. Store these in the firmware of the unit, and in a central database. Put the public serial number on the outside of the unit. You can use an openvpn login script to ensure that a particular unit always appears at the correct IP address, which keeps the proxy configuration static.
You can control openvpn's bandwidth usage by adjusting its keepalive behaviour, and how often it renegotiates. Measure and tune this before a large deployment.
The NAT timeouts in the mobile networks are generally between 5 and 15 minutes. The device must send a packet to the server often enough to keep NAT alive.
Cheap SIM deals may be web only with limited ports.
Other tips:
GPRS modem firmware can (rarely) crash internally. If your hardware supports it, provide software with the ability to power cycle the modem.
Test your box in areas with poor coverage in your own country before you send out international shipments.
This is a typical problem with "mobile agent" appearing in different places or using different providers (in this case just one provider, but it's almost the same). Usually it's solved using some kind of home agent - a server that the mobile connects to and gives details about how to reach it or if it can't be reached directly then the home agent acts as a proxy.
Client always contact the home agent first and then if it is possible they contact the mobile or if it's not they use the server as a proxy.
In some cases dynamic dns might be sufficient in other you need real proxy/ façade.
There's a good book: Andrew S. Tanenbaum & Maarten van Steen :"Distributed Systems: Principles and Paradigms"
You can ask cellular provider to give you a SIM card with internet access and fixed IP address. Then you can host any server you like. Do not forget that you are dealing with limited bandwidth.