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How to reclaim the occupied IP address-update the ultimate version

©Lander Zhang focuses on on-demand IT infrastructure operation and maintenance services for foreign enterprises, and IT Helpdesk hands-on training practitioners

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Easy entry into foreign companies: the way for IT Helpdesk engineers to practice and self-study: https://blog.51cto.com/lander/2413018

Last updated: 2019-10-12

Problem description

After a planned power outage in the factory of a foreign company, it was found that a printer in the purchasing department could not be used properly, and the IP address became empty after checking, so the original IP address (.98.54) was manually set to prompt the IP address conflict.

Judge and solve the idea

1. Locate the cause of the fault

Log in to the DHCP server and find that the IP address (.98.54) has been occupied by a certain AP. The reason should be that after the incoming DHCP server is enabled, the AP starts faster than the printer, and the IP originally used by the printer is occupied by DHCP allocation.

two。 Solution idea

Because there is a lease for the DCHP server to assign an IP address, the easiest way is to replace the AP with a different IP address or power off before configuring the original IP on the printer. As the network equipment is the responsibility of colleagues in the network group in the United States, due to jet lag, the high location of the AP is inconvenient and it is not safe to manually power down. Then we can only set the deny to the AP to get the IP on the DHCP server, and then configure the printer to reserve the original IP. The above settings will take effect after the DCHP service is restarted. After confirming that the printer is working, cancel denying AP access to IP on the DHCP server, restart the DHCP service again, and let AP get the new IP address.

Resolution steps

1. Refuse to assign IP to AP

On the DHCP server, add deny to AP to get the IP setting. Right-click AP in DCHP to get the IP address (.98.54) record-Add to Filter-Deny:

The key point is to add that the ultimate solution to recapture occupied IP

If you find that IP is occupied, you can also ping (the parameter that regular ping-a returns the machine name is also invalid), but you can't see the record in the DHCP lease and don't know what device it is, what should we do with it?

Step 1: get the MAC address

Connect your computer to the occupied IP segment, and then ping the occupied IP. For example, if the IP of.. 98.54 is occupied, and it is located on the network segment of.. 98.0, then connect my computer to the network segment of 98, and then go to ping. * .98.54:

Then use apr-a to obtain the MAC that occupies the corresponding device of the IP:

Step 2: deny IP to the device with the MAC address

Filters-Deny-New Filder...:

Enter the MAC address of the device-Add:

two。 Reserve a fixed IP for the printer

Create a new record in Reservations and enter the printer MAC address and the IP address to be assigned (. 98.54):

3. Restart the DHCP service test printer

After restarting the DCHP service, the printer grabs the original IP address (.. 98.54) according to the created reservation policy, and completes the manual configuration on the printer, which has been tested for normal use:

4. Delete deny IP setting for AP

Delete and refuse to assign IP settings to AP, restart the DHCP server takes effect, and the AP can get the IP normally after testing.

5. Follow-up measures

Check all devices that require a fixed IP address and configure reservations to prevent this from happening again.

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