DHCP Lease Page Online Column

  • What exactly is pfsense checking to show if a device is online or offline? I am making some network adjustments and was curious about what it is checking or watching.

  • @ghostshell

    DHCP leases are driven entirely by the client. When it connects, it sends a DHCP discovery, to which the server sends an offer, then the client sends a request and the server an ack. Part way through the lease time, the client will renew, by sending the request again. This continues indefinitely and the the client "owns" the lease, until it expires. It expires at some time after the client stops renewing. So, the server doesn't check if a device is online, only that there's a valid lease.

  • I understand what a DHCP lease is and how they work, I was only asking about how the online column on the DHCP Leases page works. The only part I needed from your post was "the online column show online if a valid DHCP lease is active if expired it shows offline".

  • @ghostshell

    Well, if you look in the help, you'll find:

    "The Status > DHCP Leases page only reports systems as “online” if the MAC address for a given system appears in the pfSense® firewall’s ARP table. This can be verified by checking Diagnostics > ARP Table. Systems that have not communicated with or via the firewall in the past few minutes will appear as offline."

    In order for a MAC address to be in the lease table, the device has to have communicated with the pfSense system. This could be actual traffic with it, such as DHCP, DNS requests, etc. or just being routed through it. If pfSense hasn't seen any traffic from the device, it will disappear from the ARP cache and will be listed as offline.

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