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DHCP issuing IP addresses out of range of the starting IP address.

Our router is set up to issue IP's through DHCP starting at 192.168.0.115 but for some reason people's cell phones/laptops are connecting to 192.168.0.110 automatically and we use that IP for a machine in our shop and it keeps conflicting. It's a very difficult process to change the IP on the machine, does anyone have any ideas what could be happening here?

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Accepted Solutions
Community Member

If the DHCP bindings don't

If the DHCP bindings don't show that the router gave out that IP address (it starts at 116 like you said) then those IP addresses are likely statically assigned. 

ARP/RARP table won't ever assign IP addresses. Your best bet is to find out what MAC address corresponds to that IP address (show ip arp) and then find out what switchport it is connected to (show mac address-table <MAC_Address>) and track down the device that is using that IP address.

Also, it may help for you to show the OUI of the MAC address as it may point to the vendor of the device. 

Community Member

YupPing the device and check

Yup

Ping the device and check the arp to get the Mac then you can check switches Mac table to see where the device is.  Goodluck 
6 REPLIES
Community Member

What does your config for

What does your config for dhcp look like?

Community Member

Here is a screenshot, I hope

Here is a screenshot, I hope this explains it a little better. We have the starting ip at 192.168.0.115 but you can see with my angryip scanner, there are a few machines that are at 110, 113, 114. http://imgur.com/fLzCQdS

Do I need to change something else in the router?

 

edit: We do have an access point, and a couple switches around our office but that shouldn't affect anything should it?

Community Member

Can you check the dhcp table

Can you check the dhcp table to see if that router in fact handed out the ip addresses?

Did you recently change the scope?

Community Member

Glad you said that. The DHCP

Glad you said that. The DHCP table looks fine actually, everything is 116 and up. but the ARP/RARP table is what is assigning IP's under 115. How do I fix this?

Community Member

If the DHCP bindings don't

If the DHCP bindings don't show that the router gave out that IP address (it starts at 116 like you said) then those IP addresses are likely statically assigned. 

ARP/RARP table won't ever assign IP addresses. Your best bet is to find out what MAC address corresponds to that IP address (show ip arp) and then find out what switchport it is connected to (show mac address-table <MAC_Address>) and track down the device that is using that IP address.

Also, it may help for you to show the OUI of the MAC address as it may point to the vendor of the device. 

Community Member

YupPing the device and check

Yup

Ping the device and check the arp to get the Mac then you can check switches Mac table to see where the device is.  Goodluck 
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