What happens to DHCP sessions on client devices when the DHCP server breaks down and comes online after an interval

dhcpdhcp-serveripsession

Scenario: I use DHCP server to authenticate and provide specific services to my device.

  1. Everything is working well, my client device has a valid IP address
    192.168.0.2 and a QoS service assigned by the DHCP server.
  2. My DHCP server breaks down, device still holds on to the IP address
    192.168.0.2 because of the available lease time and is able to communicate with other devices in the network.

I would like to know what exactly happens when the DHCP server comes online again. Will the DHCP server know about the DHCP state held by my client device along with the granted QoS service? Or will the device have to be authenticated again in order to avail the QoS service?

Any help or information on the above would be highly appreciated.

Best Answer

Normally the DHCP server would have saved its lease data to persistent storage, so after coming up again it would indeed know about the state of your client device. If however the breakdown was such that the lease data was lost then this would not hold and the server would come up knowing nothing.

If the DHCP server does just assign the QoS service together with the lease and be done with it then the device can continue using the QoS service until the lease expires even though the DHCP server may have forgotten about it. When the client device renews the lease it will also be assigned the QoS service again and all is well. If however the DHCP server plays an ongoing role in providing the QoS service even between lease renewals then the device may actually lose the QoS service until it renews the lease. This depends on the details of how that QoS service is implemented.

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