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If two systems have the similar MAC address what will the switch do

By kr_kirru ·
If two systems A&B have the similar MAC address and system C is trying to pig A. Assume both A & B had unique ip address and all the 3 machines are connected to a switch. Then will the switch do? How it functions and takes the decision?

We can change the MAC address if it comprises of EPROM. So rule out the issue that we cant change the MAC address. Try to figure out the exact answer. How does the switch takes decision when it encounters such a situation?

Check this link to change the MAC address for a linux machine(If u'r NIC supports).
http://www.linuxsecurity.com/docs/Hack-FAQ/data-networks/change-mac-address.shtml

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Are you looking for an Answer?

by JimHM In reply to If two systems have the s ...

Question for you:

Is this a question you want answered, or is this a question you are going to ask your students, or better yet the person supply the best answer is offered a position at your company as the Network administrator.

This reads like an interview question I was given once - or this one I was asked - "What steps would you take to secure a new Internet server, assuming that the company has never been connected to the internet before?"

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the switch would....?

by mungujakisa In reply to Are you looking for an An ...

yes, it's like a question asked in interview. I suppose the "not too intelligent" switch will just have to assume that these two nodes with similar mac addresses are conflicting, and so the consequences of conflicting stuff is in action. Though I think the switch will just forward datagrams meant for that mac address to both, since it has the capability of multicasting. Could you try this out and see? it might be interesting.

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I would venture that it would reject

by JimHM In reply to the switch would....?

Even if the router had intelligence in it - I would make an assumption that it would not be smart enough to determine which of the two MAC to send the traffic. The sender would receive a message to the effect that there is a duplicate address - and reject the PING or other attempts to communicate.

If you do it by the IP (Which was different)it should make it. I know back in the days of the IBM Networking with NetBios and NetBeui (which was sold to MS) that a duplicate MAC was rejected.

I can't see how duplicate MAC Names or addresses would survive on the same network. Unless fully qualified with the IP address or a unquie identifier... and if you are doing that - why not make it simple and change the MAC address.

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Depends on the switch

by gralfus In reply to If two systems have the s ...

Sure sounds like someone's homework problem. And this has been posted to the Tech Q&A already.

Some switches are more intelligent than others, and some just have more capabilities built into them than others. Some switches would broadcast to both ports since the lookup table will list both ports for that MAC. Multicasting is a technique that purposefully uses the same MAC on multiple servers and the switch can load share between them, if it is the right kind of switch. So it depends on the kind of switch and what your tell the switch to do with it. If the switch has both MACs in its lookup table at the same time, it will most likely broadcast to both ports.

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Is this a Test?

by CG IT In reply to If two systems have the s ...

I saw this question under technical Q&A.

Have to question the motive behind posing a senario like this. IMO is spam!

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Another swipe

by CG IT In reply to Is this a Test?

I do have to take another swipe. I can't resist it. Questions that propose a senario like this reminds me of a joke George Carlin once did. He was raised Catholic and he and his pals would jokingly ask the priest these seemingly contradictory senarios such as : "If god is all powerful can he make a rock so big he can't lift it".

If 2 computers in the same network both have the same MAC address what will the switch do? Knowing that RFC says no 2 NICs can have the same physical address when mfg'd on the surface the question seems moot. Yet cloning MAC addresses have been around a while. Biggest question is, Why on earth would you go through all the trouble unless your endeavor is for mischevious behavior. Clone someone's MAC address and your essentially that computer. You can conduct all manner of stuff and the blame falls on someone else.

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