I am trying to make a software that would use computers in my local subnet who are also using the same software that I am making. Regarding this, I want to know how I should scan my device to find 1) devices in my local subnet, 2) devices in my local subnet that is using the software? Any idea on this will be appreciated.
Thanks in advance.
OS? Programming language?
For Windows and C#/VB you can use this example.
In general, all instances of your program should start listeners on some IP port.
Every listener waits a request, then sends an answer.
To locate all instances in local network your program must send broadcast request to the same port and wait for answers.
You can google example of UDP broadcasting for your platform (OS and programming language) for more details.
Related
I am trying to understand the concept of port number. As much as I know it identifies a specific process or a network service.
Can anyone give me a real life example. So, it could be easier to understand.
Some doubts that I currently have-
I heard, there are 65536 ports. Does, that mean, a system can identify 65536 processes simultaneously?
I have seen that some ports are reserve for some specific service. So, does it mean, it can't be used for any other service?
What is the command to know which port numbers are free or to use?
What is the command to know which port numbers are not free and what are they used for?
If I try to access a system through remote desktop from my computer, it asks for a port number. What should I mention?
If possible please share a link. I am currently getting confused with too much technical theory. Thank you!!!
I heard, there are 65536 ports.
You heard wrong. There are 65535: 1 .. 65535. Zero is not a valid port number.
Does, that mean, a system can identify 65536 processes simultaneously?
It means a system can identify 65535 ports simultaneously.
I have seen that some ports are reserve for some specific service. So, does it mean, it can't be used for any other service?
That is the meaning of the word 'reserve'.
What is the command to know which port numbers are free or to use?
It isn't a command. It is either a search at the IETF website for reserved ports or the use of the number zero, which means the next available port.
What is the command to know which port numbers are not free and what are they used for?
It isn't necessarily a command. It is a search at the IETF website for reserved ports, or the netstat command for ports actively in use on the localhost.
If I try to access a system through remote desktop from my computer, it asks for a port number. What should I mention?
The port number that you're trying to connect to in the remote system.
Here is more clarification:
I heard, there are 65536 ports.
A port is 16 bit i.e. 2^16 =65536 so right
"Port Zero does not officially exist. It is defined as an invalid port number. But valid Internet packets can be formed and sent over the wire to and from port 0 just as with any other ports." https://www.grc.com/port_0.htm
Does, that mean, a system can identify 65536 processes simultaneously?
You do not care about a system, you care about an IP. For every Ip you can use 65536 processes simultaneously.
I have seen that some ports are reserve for some specific service. So, does it mean, it can't be used for any other service?
Of course, otherwise there will be a port conflict.
What is the command to know which port numbers are free or to use?
Refer my post here https://stackoverflow.com/a/54760498/2197108
Netstat: in Linux and Windows displays connections and ports
What is the command to know which port numbers are not free and what are they used for?
It should be clear now
If I try to access a system through remote desktop from my computer, it asks for a port number. What should I mention?
Remote desktop asks for IP address of the remote machine. However, it may ask for user credentials of the remote machine.
In case it asks for IP and Port it means IP and Port of the remote desktop software (server) in the remote machine.
I'm app developer from Korea.
Let me have one supposition.
There is one PC and one android tablet.
these devices are in same network.
(192.168.0.x ...same in C class)
My question is same as followings
"using PC, how can I find another device by the device's MAC address only?"
I know there are network protocols including UTP , TCP/IP ....
which one should I use ?
and What algorithm should I use?
Please Help.
Thank you so much for reading.
I would suggest just passively listening until the device sends a packet. As soon as you see a packet with that MAC address as its source, its source IP address will (most likely) be that devices IP address. The specifics of how you promiscuously monitor a network vary by operating system.
The most portable way to do it is probably to attempt to communicate with ever IP address in the subnet, checking the operating system's ARP table to see if you found the right MAC. This requires non-portable code only to pull the ARP table. It's unpleasant if you happen to find yourself on a /16 subnet -- that's over 65,000 IPs with broadcast traffic needed for each one of them.
There's probably a better way to solve your outer problem, whatever it is.
I'm writing a mini OS just for fun. I want to save some key information to one securiry server on the Internet and ever fetch it BEFORE booting my OS.
So my problem is: How to access the Internet only via BIOS? i.e. How to use the TCP protocol in BIOS environment?
PS.
It is obvious that diskless workstations use such a technique. So it is technically possible.
Diskless workstations use PXE which is part of NIC (network card) ROM or a BIOS extension, it's a simple environment that implements TCP/IP stack that can get a executable over TFTP and run it.
There is an open source one that you could modify iPXE to your needs and replace your existing PXE ROM.
I don't think that this is possible. You need to implement a network driver into the BIOS to achiving that. So I would say this is not possible. By the way I never read that someone wrote his/her own BIOS.
If you have an ethernet port on your pc/router buy a Gil.Net router and connect it wirelessly to your home router and then plug in the router
I would like to write a software running in a networked device, i.e. PC. It can automatically detect the other network devices' types. For example, it can detect there is a PS3, a Wii, an IPad running in the same network. Any ideas? Thanks,
You have two problems: first, detecting that a device is connected to your network and at 192.168.1.x. Second, somehow detecting what that device is.
The first is easy-ish to accomplish: there's discovery protocols like UPnP and Bonjour. However, in a home networking scenario, the easiest and most reliable way to get a list of connected devices is probably to pull the DHCP reservations from your router. You might have to scrape data from the router's HTML-based management interface—hacky as that may be—but it would work. (If you're using .NET, consider the HTML Agility Pack to accomplish this.)
Once you have a list of IP addresses of connected devices, your next problem is to figure out what each device actually is. This will be more challenging. Some possibilities:
You may be able to use the MAC address to help detect the device's vendor. (Here's a list.)
If you're using UPnP, you can ask the device what it is.
Use IP fingerprinting to determine what the device is.
Couple thoughts. The broadcast IP address - 255.255.255.255 is where devices talk and say "here I am". Should be able to listen to this and find ip addresses and more. Second, if devices are assigned an IP address by a DHCP client (obviously) you can usually find a list on the dhcp device. Devices often have names, this is a higher level protocol, like windows SMB, that you may have to interface with in order to get that information.
I'm working on a Wake on LAN service that will run from a web site and should interact with many different platforms - therefore, no Windows-only solutions. When a user registers their system with the web site, I need to get the MAC address to use in constructing the "magic" packet. I have a Java Applet that is able to do this for me and am aware of an ActiveX control that will work, but I'm wondering if there is a way to do this server-side by querying routers/switches. Since the system may be on any of a number of different physical subnets, using ARP won't work -- unless there's a way to configure the router(s) to perform the ARP on my behalf.
Anyone know of any network APIs, proprietary or otherwise, that can be used to look up MAC addresses given an IP address? I think we're using Cisco routers, but it's a complicated network and there may be multiple vendors involved at various levels. I'd like to get some background information on possible solutions before I go to make a sacrifice to the network gods. No point in abasing myself if it's not technically possible. :-)
EDIT: We do have the network infrastructure set up to allow directed broadcast, though figuring out the exact broadcast address since netmasks are not always /24 is another conundrum that I need to solve.
If you are on a local network that uses DHCP you might be able to look in the servers database to get the MAC of the last user with that address. In the future you could watch the network for ARP requests and cache the responses in some sort of table. You might also look at using RMON or SNMP to try and query the Address Tables on the switches and routers.
It should be noted that to use WoL across routers you either need to enable Directed Broadcasts or you need to have a relay server in the local segment.
Been a while since I played routers and swtiches but this might be a starting point for what to query using SNMP http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a00801c9199.shtml
Use the following:
getmac /s destIp
To get the remote session Mac address.
I don't know if these might be helpful but take a look:
http://www.webdeveloper.com/forum/showthread.php?t=134120
http://www.qualitycodes.com/tutorial.php?articleid=19
You've said everything I can think of...
The source MAC address changes as a packet hops from device to device so unless the client is on the same subnet, the server won't be able to get the MAC address. (You would do it via ARP)
A signed java applet or activex control would be the easiest solution. It would be able to (almost passively) get all the networking info you need (IE doesn't even prompt to run a signed applet)
If you are fully aware of the network that is using the service then you could probably query a gateway's client-list via SNMP or CDP. You would be able to map out IP-Addresses to MAC addresses... but this is really vendor dependent (but common) and wouldn't be much better (imo) than having an applet.
Currently the application is using a Java 6 applet that allows me to extract both the hostname and the MAC address from the remote system. I don't like having this dependency on Java 6, but Snow Leopard and Windows both support it, so I can probably live with it.
On a related-front our networking folks approached me for some help with converting some existing code to ASP.NET. During the conversation I asked if they had live MAC address information (since they do port shutoffs based on suspicious network activity -- viruses/worms). Turns out they do and we may be able to leverage this project to get access to the information from the network database.
I don't think there is any way to accomplish this. When the IP packet goes via the first router the host's MAC information is lost (as you know MAC is only used in ethernet layer). If the router most close to your PC was capable of telling the remote MAC code to you, again it would only see the MAC of the next router between your PC and the "other end".
Start sacrificing.
There's no general way to do this in terms of the network unless you have no routers involved. With a router involved, you will never see the MAC address of the originating system.
This assumes that the originating system only ever has a single network interface, so has only a single MAC address.
In fact, are you even sure that your "magic packet" (whatever that is) will reach the system you want it to reach, through the routers? That sounds like a function the routers or other network infrastructure should be performing.
Mac address is only used on network segments, and is lost at each hop. Only IP is preserved for end-to-end - and even then the from ip address is rewritten when Natted. I guess my answer is, not possible unless everything is on the same network segment, or your routers are set up for proxy arp (which is not really realistic).
You can only get MAC entries in the ARP table for machines on the same network. If you connect to a machine via a router then you will only see the routers MAC address in the ARP table. So there is no way of knowing the foreign host’s MAC address unless it's a host on the same network (no routers involved).
And by the way there are many similar question already on SO.
if it's a windows system you can use NBTSTAT -A
this will return the netbios info and the IP is there
any Management system like SMS or Altiris will have this info
The DHCP server is a good idea
If it's local you can ping it and then quickly run ARP -a
look for the IP and the MAC will be there.
you might need to write a small batch file.
if you have access to the PC you can use WMI to access the info for the Nic with DHCP.
As said above we can get mac address from a known IP address if that host is in the same subnet. First ping that ip; then look at arp -a | grep and parse the string on nix* to get mac address.
We can issue system command from all programming languages standard API's and can parse the output to get mac address.Java api can ping an IP but I am not sure if we parse the ping output(some library can do it).
It would be better to avoid issuing system command and find an alternative solution as it is not really Platform Independent way of doing it.
Courtesy: Professor Saleem Bhatti