luanncross
1 Nickel

MAC Addresses - Can there be duplicates?

We have a network of over 100 PC's with all fixed IP Addresses.  We provide a limited number of DHCP addresse for our laptop users. 

The problem is that at various times during the day , night and week-ends, the mac address associated with the LAN adapters on two particular PC's, a Dell Optiplex 170L and a Dell Optiplex 780 , are going out and also grabbing DHCP addresses.

Anyone know what this could be.  Is it the PC's other hidden network adapters that are grabbing DHCP addresses, or could there really be duplicate MAC addresses on other devices?

I regularly monitor the DHCP logs.  The MAC addresses appear, renewing a DHCP address but with no identifier.  "Renew,192.13.10.120,,001E4FF57808".  This MAC address is also the MAC address for the PC's Network LAN Adapter.

 

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16 Replies
7- Gold

Re: MAC Addresses - Can there be duplicates?

Hi Luanncross,

Let me suggest you try posting this question in the networking forum.

Good luck!

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luanncross
1 Nickel

Re: MAC Addresses - Can there be duplicates?

You know, that was not a useful reply. 

I went to your network forum, I read the "PL:EASE READ THIS FIRST BEFORE POSTING TO THIS FORUM".  The guy said

"The purpose of this forum sticky is for forum members to suggest and give you helpful tips on getting your wireless devices working. So let's keep those suggestions coming in."

My problem has nothing to do with wireless devices.  However, to satisfy all concerned I will re-post in Networking.

Can we stick to doing the work, and not the politics please. 

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muto
3 Zinc

Re: MAC Addresses - Can there be duplicates?

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RoHe
6 Indium

Re: MAC Addresses - Can there be duplicates?

@muto, @luanncross -  

You've both mouthed off about one of the Dell Community forum's VIPs who has over 35,000 posts helping people fix their PC problems. If you can't say something nice, keep it to yourself.

And if you don't like the FREE help you get here, take your silly problems elsewhere... 

Ron 

Ron

   Forum Member since 2004
   I am not a Dell employee

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muto
3 Zinc

Re: MAC Addresses - Can there be duplicates?

.

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luanncross
1 Nickel

Re: MAC Addresses - Can there be duplicates?

I really don't have any further information about our network configuration that would be useful.  I manually set the IP addresses of each PC in the properties of the LAN card, TCP-IP section, including gateway and primary, secondary servers.  I have tried to do the DHCP reservation idea, but we are so short on DNS and DHCP addresses it wasn't useful.

I didn't enter the forum to upset anyone, I just wonder why my fixed address machines are grabbing DHCP.  That's it. Thanks

 

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8 Krypton

Re: MAC Addresses - Can there be duplicates?

Make sure your static IP address assignments are not part of the router's DHCP pool (i.e., if your router assigns 192.168.1.1-50, use 192.168.1.51-100 for the static ones.

 

 

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muto
3 Zinc

Re: MAC Addresses - Can there be duplicates?

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luanncross
1 Nickel

Re: MAC Addresses - Can there be duplicates?

Thanks everyone for their comments.  I have been in computing and networking for over 20 years.  I do understand and recognise what you are saying.  I have identified and blocked every unknown user from our DHCP.  I have not mistakenly used our DHCP range of addresses and assigned them  as a fixed address.  The reason for monitoring the DHCP logs was to ban factory workers from bringing in their own PC's, XBoxes, IPads, IPhones and using them because someone gave out our WEP keys.  I have managed to stop all of that traffic.

As I said in my original post.  There are only 2 DHCP users that are not identified, they show no identifying name in the DHCP log.  there are two commas where that would normally be.  The MAC addresses are those of existing fixed IP PC's. 

Simply, If I can figure out why these PC's, if in fact they are PC's, are taking two of my limited number of DHCP addresses when they already have assigned IP's on their LAN adapter.  It is a problem I have not come across before, and I find it a challenge to figure it out.

 

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