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OrbiPhilip's avatar
OrbiPhilip
Luminary
Mar 05, 2020
Solved

DHCP reservations not working

Yesterday I added a raspberry pi to my network (running Nagios/NEMS). Every time it rebooted it took the next IP in sequence. That shouldn't happen... Instead of fighting with it, I created a reserva...
  • tomschmidt's avatar
    tomschmidt
    Mar 05, 2020

    I likewise had this issue, and a reboot of the router corrected it.  I reported the issue to NG support, and they claimed the system firmware is "glitching" causing this.  They admit that the firmware is still a bit buggy with v2.5.1.8 on the RBR50, but have no ETA on when they will have a stable and reliable mesh network.

CrimpOn's avatar
CrimpOn
Guru - Experienced User
Mar 05, 2020
OrbiPhilip wrote:

That was the first thing I checked.  MAC is consistent.  Reboot fixed the problem, but the DHCP entry still does not appear in the logs.

Can you please clarify:

  • The Orbi log contains DHCP assignments for every device except this one, or
  • The Orbi log contains no DHCP assignments for any device

Thanks

OrbiPhilip's avatar
OrbiPhilip
Luminary
Mar 06, 2020
Can you please clarify:
  • The Orbi log contains DHCP assignments for every device except this one, or
  • The Orbi log contains no DHCP assignments for any device

 

Before reboot the log contained many DHCP entries in the form of:
[DHCP IP: 192.168.1.xx] to MAC address xx:xx:xx:xx:xx:xx, Friday, February 21, 2020 17:35:58
Not none matched the IP or MAC of the Pi.

After reboot I connected to the Pi on 192.168.1.59 and rebooted it. It leased the address listed in the reservation (192.168.1.56). The log after reboot contains *no* DHCP entries. 

  • OrbiPhilip's avatar
    OrbiPhilip
    Luminary
    Mar 09, 2020

    One problem that the Orbi system seems to have is the lack of ability to manually drop a DHCP entry from the table. As such, any device getting a DHCP address will continue leasing that address until the router is rebooted. 

    This is especially problematic when you give a device (including the Satellites) a DHCP reservation for an address other than the one auto-assigned. Anytime a given MAC is added to the reservations list, it should be dropped from the database if the IP changes.

    • CrimpOn's avatar
      CrimpOn
      Guru - Experienced User
      Mar 09, 2020
      OrbiPhilip wrote:

      One problem that the Orbi system seems to have is the lack of ability to manually drop a DHCP entry from the table. As such, any device getting a DHCP address will continue leasing that address until the router is rebooted. 

      This is especially problematic when you give a device (including the Satellites) a DHCP reservation for an address other than the one auto-assigned. Anytime a given MAC is added to the reservations list, it should be dropped from the database if the IP changes.

      I concur that this appears to be what happens.  I do not know if it is a coding issue or if Netgear is following some "industry standard behavior" that I have yet to find.  To MY mind, when the administrator creates an IP reservation for a MAC address, the system should immediately force the device to that IP address by sending  A brief search for DHCP standards documents reveals:

      RFC 1541 (1993) https://tools.ietf.org/html/rfc1541 

      RFC 2131 (1997) https://tools.ietf.org/html/rfc2131 

      RFC 3203 (2001) https://www.ietf.org/rfc/rfc3203.txt 

      This document defines extensions to DHCP (Dynamic Host Configuration
   Protocol) to allow dynamic reconfiguration of a single host triggered
   by the DHCP server (e.g., a new IP address and/or local configuration
   parameters).  This is achieved by introducing a unicast FORCERENEW
   message which forces the client to the RENEW state.

      In the "Linux world" once modules are coded, there is little interest in reworking them.  My GUESS is that the DHCP code in OpenWRT (the basis for Orbi) simply does not incorporate this RFC.

       

      Every time this phenomenon "bites me", it is a real chore to restore order.  I keep an old cell phone for this purpose.

      • Turn off the offending device that has picked up the wrong IP.
      • Go into the LAN web page and assign that wrong IP to the cell phone.
      • Power up the cell phone and connect.  Now the cell phone is on that IP because when Orbi ARP'd, nobody said, "Hey, that's me."
      • Now, power up the offending device.  It asks for an IP.  Orbi sees that it doesn't have one.  Orbi gives it the IP out of the table.
      • Cell phone goes back in drawer until next time.
      • FURRYe38's avatar
        FURRYe38
        Guru - Experienced User
        Mar 09, 2020

        I notice that when I do any IP address reservations, Add then save then Apply, the RBR reboots by default. So this should take effect and should clear out any unused IPs.