Finding static IP addresses of exisiting devices with a new router



  • My primary PFsense router died yesterday, and knowing this day might come I had a backup router waiting in the network rack, flashed with the same config ready to go in case this day ever came. I turned it on and internet was restored in about 5 minutes.  :D

    My victory was short lived as while the internet is working. The last backup I had was 6 months ago :( and I had added several new devices with static IP addresses since then. Now those devices are still working and I am able to ping those devices, but they are not showing up under the DHCP leases tab in the Pfsense admin panel.

    Currently, the only way I know of to get a new device to show up in the DHCP leases of the Pfsense admin panel is to wipe the static IP of the device, and let it grab a new IP address from the DHCP pool and then assign the static IP address.

    My question is there a way for the Pfsense router to detect the current static IP addresses on the network without me having to repeat the above process on every device?

    I attached some screenshots for a visual example of what I am talking about. The printer IP is 10.2.111.28 and it responses to a ping test, prints, and I can access the web portal, but it does not show up in the Pfsense DHCP leases.







  • No, there isn't.  However, why are you going through all that trouble.  Instead of assigning static addresses, why not just map an IP address to a static and leave it like that?  Other than my main desktop computer, I do that for all my other devices.


  • Galactic Empire

    You could run nmap and do a scan of the subnet, that should give you the mac address to IP address so then you could update your DHCP reservations.

    [2.4.2-RELEASE][admin@pfsense]/root: nmap -sP -PR 172.16.2.0/24

    Starting Nmap 7.40 ( https://nmap.org ) at 2018-01-26 13:18 GMT
    Nmap scan report for timecapsule.xxxxxxxxxx.net (172.16.2.6)
    Host is up (0.0015s latency).
    MAC Address: 6C:70:9F:D8:3B:4E (Apple)
    Nmap scan report for nas.xxxxxxxxxx.net (172.16.2.10)
    Host is up (-0.20s latency).
    MAC Address: 00:11:32:4C:81:69 (Synology Incorporated)
    Nmap scan report for pi-2.xxxxxxxxxx.net (172.16.2.11)
    Host is up (-0.20s latency).
    MAC Address: B8:27:EB:EE:7F:AA (Raspberry Pi Foundation)
    Nmap scan report for mac-pro.xxxxxxxxxx.net (172.16.2.20)
    Host is up (0.0034s latency).
    MAC Address: 00:3E:E1:C1:AF:07 (Apple)
    Nmap scan report for w7-vm.xxxxxxxxxx.net (172.16.2.30)
    Host is up (0.0061s latency).
    MAC Address: 00:50:56:29:C2:92 (VMware)
    Nmap scan report for iphone.xxxxxxxxxx.net (172.16.2.40)
    Host is up (0.00090s latency).
    MAC Address: 40:9C:28:A2:E0:7E (Unknown)
    Nmap scan report for mu-so.xxxxxxxxxx.net (172.16.2.55)
    Host is up (-0.085s latency).
    MAC Address: 30:10:B3:F4:3F:90 (Liteon Technology)
    Nmap scan report for 172.16.2.101
    Host is up (0.098s latency).
    MAC Address: 54:E4:3A:F1:76:A1 (Apple)
    Nmap scan report for pfsense-user.xxxxxxxxxx.net (172.16.2.1)
    Host is up.
    Nmap done: 256 IP addresses (9 hosts up) scanned in 4.03 seconds
    [2.4.2-RELEASE][admin@pfsense]/root:

    I do DHCP reservations to nearly all my devices, its much easier in the long run IMO.

    They should also be in the ARP table if you can ping them.

    Diagnostics -> ARP Table



  • You could run nmap and do a scan of the subnet, that should give you the mac address to IP address so then you could update your DHCP reservations.

    Nmap has to be installed first.



  • Thanks for the responses guys. I haven't used nmap before and provided all sorts of useful information. As to why I was doing that was keeping my DHCP addresses and static addresses separate. It's an old habit. Mapping to IP addresses does make things easier.



  • Diagnostics - ARP Table will give you a list of clients that pfSense has seen lately, and compare that against your dynamic range.



  • @KOM:

    Diagnostics - ARP Table will give you a list of clients that pfSense has seen lately, and compare that against your dynamic range.

    Arp caches delete entries in a fairly short time.  Also, it requires the pfSense computer to actually receive frames from the devices.