Detect duplicate mac address linux

Here is what the forged package looked like: Here is what the reply looked like: If you watch the responses and see your MAC address in one of the packets in the red rectangle , than someone has the same MAC address as you do Unfortuantely I couldn't test the theory fully because none of my Windows machines care about me trying to set the nic's MAC address Two hosts using same MAC address on a single network segment would probably make switches go nuts and you could probably detect it by having an extremely unreliable network connection as the switches would send some portion of packets that belong to your host to the second one, depending on which one of you sent the last packet in their direction.

This is very late, and a non-answer, but I wanted to follow up with exactly what I did in case anyone else is interested. That means we needed to assign one in software. However, I wanted to pick a reasonably safe default, and also attempt to warn the user if a conflict occurred. In the end I resorted to picking a random-ish default in the locally-administered range, chosen by making some hardware readings that have moderate entropy.

What Happens when there are duplicate MAC Addresses. How many MAC Addresses can a Switch learn?

I deliberately excluded the beginning and end of the range on the assumption that those are moderately more likely to be chosen manually. The chances are that there will only be one of these devices on any given network, and certainly less than 20, so the chances of a conflict are very low, albeit not as low as they could be due to the somewhat predictable random numbers.

Given the low chances of there being a problem, and despite the excellent answers above, I decided to dispense with the conflict detection and make do with a warning to the user to look out for MAC conflict problems. If I did decide to implement conflict detection, then given that I control the whole network stack, I would probably look out for excessive unknown or missing packets, and then trigger a change of MAC address or warn the user when that happens.

By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies. Daniel Cassidy. Daniel Cassidy Daniel Cassidy I haven't found a definitive answer, but here's my thought process, in the hope that it helps: What sort of protocol fits this description?

Easy Answer: You may need to be creative to force the packet onto the wire and prevent yourself from responding I'm thinking judicious use of iptables and NAT. Not-so-easy Answers: Adam Liss Adam Liss Thanks for this excellent response. I will definitely be following up.

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What Happens when there are duplicate MAC Addresses

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How to find IP address and MAC address on ubuntu systems

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Related They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own. Click Here to receive this Complete Guide absolutely free. Hi, someone asked me how hard it would be for a typical university's network people to detect MAC address spoofing. He was getting bandwidth warnings saying that he has used more than five standard deviations of the mean. Since you're required to register your network card before you can access the university's LAN, I guess anytime you plug your computer in, it will know who the computer is registered to based on the MAC address.

So will falsifying the MAC address go unnoticed for the most part, or does the network automatically check for duplicates. If it finds a duplicate, what is the normal course of action? BTW, nothing illegal is intended, just good old fashion privacy. This is very easy to do, simply alter the mac of the network card, or if its built in the motherboard. Duplicates, are not always detetected, depends on what their using for authentication.

I suspect that they would have duplicate detection going on, also they may only authorise MACs to certain locations.

Your probably not the first to think of this. Also they may have had problems in the past with multiple devices having the same MACs cheap mass produced stuff, sent out with the same MAC. Theres a lot to think about with this. Find More Posts by leonscape. This little utility might help http: Gerneally speaking what happens when you have 2 duplicate MAC addresses on the network is that everything will still work, with the only exception that these 2 devices with identical mac addresses won't be able to talk to each other.

Duplicate mac addresses with different ips in the arp table is valid to most operating systems, and it goes undetected because ARP protocol is stateless ie it'll accept any arp broadcasts, even if it didn't request it unless you deliberately try to detect them. Last edited by Demonbane; at It gives an university campus WAN with more than 2 buildings but for the moment building A and building B that is enough.

I ask for location they say that will investigate. How can I trace it in an WAN?

What Happens when there are duplicate MAC Addresses. How many MAC Addresses can a Switch learn?

If I were a mod, I'd cut this last post out and create a new one maybe. S3TH76, You might use tools like arp, wireshark and maybe a few others to watch data. From there you might be able to get an IP address. In actuality you can use arp to make a static ip address with this unknown mac. Then see if you can get any data off it. From the prior posts, you can see that a single user may be duplicating the mac. In a strange possibility one could in fact at some time be on a lan with a real, duplicate mac.

There aren't enough mac addresses. Thread Tools. BB code is On.

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