I recently found out that some ethernet modules like enc28j60 provide api for mac address assignment. I was surprised because I thought the manufactor will assign this address in unique way. So, what is the way to solve this problem? I know, that in the case of private local networks manual assignment will solve this problem (probability of collision is small). But it is interesting for me about other ways to cope with it. Theoretically I can suppose some algorithms:
Device can assign part of mac address in random way after reset. Reseting can be automatic.
There is server, which supports some connection with enc28j60. It scans network and will assign unique mac address.
Mentioned above methods have drawbacks if sometime device with the same mac address will be appeared
Just to buy some range of mac addresses for personal use
Related
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.
For a classification project I'm trying to generate a large list of dynamic IP addresses from a single wireless network. However, the only way I've been able to generate these addresses is by connecting a physically new machine to the network, as the wireless network remembers each machine (and so, whenever one machine rejoins the network the IP address remains the same).
For the sake of brevity, I've been looking for a way of automating the process; technically, all I need to do is find a way to simulate being a "new" machine. This way, it would be far easier to generate a list of IP addresses assigned by a single wireless network.
I've had a great deal of trouble finding out how to do this, and it is very possible I may misunderstand how a wireless network assigns IP addresses, etc.
Thanks!
(continuing from the comments above...)
As it turns out, there's no fancy machine learning necessary at all. You can get all the information you need by connecting just once. When you connect to an IP network and are assigned an address, you get both an address and a subnet mask (look it up if you're not familiar with the terms). Given these, a straightforward snippet of bitwise arithmetic will show you whether another address is part of the same network or not:
if ((my_address & subnet_mask) == (unknown_address & subnet_mask)) { ...
where unknown_address is the address you're testing. (This expression can be simplified a bit by applying boolean simplification rules, but this is a form where it's obvious what is happening.)
For example, if you are assigned:
address: 192.168.11.22
subnet: 255.255.255.0
then any other address is part of the same network if it starts with 192.168.11.. Again, the person who set up the network has very deliberately made these choices.
This very much reminds me of the so-called Barometer question, where one of the possible answers is "trading the barometer to the building's superintendent in return for the information wanted".
Why do we need an IP address when the MAC address is unique? Cant we communicate only with the MAC address?
You COULD communicate using only the MAC address, but only on your local network. IP addresses are routeable, without every system on the network needing to know about every other. You just need to know a range of addresses that are on your local network, and throw everything else up to your router. The same thing happens at the ISP level. "All 216.x.x.x traffic goes that way, all 105.x.x.x goes that way..."(Obviously a gross oversimplification, but that's the basic process).
If we tried to route everything by MAC address, every machine on the network would have to maintain a list of every other participant, and it just wouldn't scale.
No. MAC addresses are specific to Ethernet, IP is independent of the underlying hardware. You can connect machines that don't use Ethernet to the Internet, if you have the required bridges.
MAC addresses are not unique. MAC addresses are reused between media. This is why wireless (802.11) and wired (802.3) may not both be present on one collision domain (see 802.1D).
MAC addresses are not clustered -- meaning that devices which are nearby in network space do not have nearby MAC addresses. IP addresses do have this property of locality. Do you intend to route packets by having a universal list of MAC addresses copied to every computer on the Internet, or do you intend to route packets to their destinations through a hierarchy of localities?
On a single collision domain, MAC addresses can be the primary addressing mode (q.v. arp and rarp). However, extension to multiple collision domains is ineffective for the above reasons.
A great professor of mine named George Varghese, now at UCSD, made the following apt analogy: You want to send someone a letter. The analogy of sending to a device anywhere in the USA based on its MAC address is like sending someone a letter knowing only their Social Security Number. It does uniquely identify someone (OK, yes, SSN isn't guaranteed unique, but suppose it was for the sake of example), but it would be very hard to find them without some giant table of where everyone lived that you could look up indexed by their SSN.
An IP address (and the similar Open Systems Interconnect, or OSI, network addresses) are more like USA phone numbers with area codes and exchange numbers: (AAA) BBB-CCCC, where AAA is an area code, BBB is an exchange number, and CCCC identifies an individual line at that exchange. There is hierarchical information encoded in that number, so that when you are far away from the destination, you only need a small table indexed by area code to determine a good "next hop" to forward the call to, rather than a table of all phone numbers in the country.
Ethernet is a Medium Access Layer protocol. It was designed specifically to connect computers on the same network. If you want to connect computers remotely located, you certainly need to jump to destination by hopping through several routers. IP (Internet Protocol) was designed with this goal in mind, hence the need for it, while Ethernet protocol does not support routing. Only some forms of primitive bridging that would not scale for something huge like the Internet.
they are used for different protocol layer.
MAC address is your device specific address. It has no relation with the geographical location, etc. you are in currently.
Ex: You can buy a cellphone/laptop in US and use it in Japan,
Australia, etc. But MAC address would remain the same. But IP address
would change with respect to the network you are connected to.
So it is difficult to route packet in an internetwork of portable devices especially.
How would it be:
Consider you have a portable network-accessing device with you on which you are using the internet. If we use only the MAC address, how would any incoming packet find the location of your portable-device. Since MAC address gives you only a fixed 48-bit device address. (The worst case scenario is using a desktop computer and having a MAC address without the IP facility. Coupling it with the static table to find your predefined location based on the MAC address, but our life is incomplete without these portable devices right?)
Thus we need some addressing scheme that can help us with addressing in a big and portable environment like internet, and thus the role of IP comes into picture, where address is hierarchal to provide a more geographically exact location.
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
I remember years ago my friend and i were playing command and conquer red alert and there was a mode were we put the others phone number and the game would dial up and connect. What was this called? and where can i find resource to program for this?
Dial-up Networking perhaps. You will have to learn how to control the modem. I remember there were some commands that looked like this: ATH0++ which was how you could make the modem do different things. Perhaps that will give you something to search for.
This resource looks kind of helpful: http://www.activexperts.com/activcomport/tutorials/modem/
One issue you might find is that there are two types of modems generally. One is an actual modem which is connected to your serial port. The other is what is typically known as a "winmodem" which is usually in a PCI slot and didn't have all of the functionality on the hardware but instead used the hardware drivers which typically only worked in Windows. MODEM stands for "MOdulator DEModulator" which means it just converts a digital signal to analog and vice versa.
In essence, it seems that if you can figure out how to program to the serial/com ports on your computer, you should be able to access the modem.
Another interesting link: http://en.wikibooks.org/wiki/Serial_Programming:Modems_and_AT_Commands
Have a look at TAPI (Telephony API). In Windows world there is a set of APIs in the OS for this (http://msdn.microsoft.com/en-us/library/ms737219(VS.85).aspx). The AT command set (Hayes commands) can also be used without TAPI in Windows if you treat your Modem as a COM port and send AT commands to that COM port (that's what actually TAPI does) but it isolates you from their different variants and also running initialization and other commands in a particular order.