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My D7800 shows repeated DHCP Allocations for the Same Device

TerryJColes
Luminary

My D7800 shows repeated DHCP Allocations for the Same Device

We have just noticed that, according to the logs, my D7800 is repeatedly allocating the same IP Address to the same device.

 

I've not noticed this in the past.

 

Any ideas?

Model: D7800|Nighthawk X4S – AC2600 WiFi VDSL/ADSL Modem Router
Message 1 of 10
antinode
Guru

Re: My D7800 shows repeated DHCP Allocations for the Same Device

> [...] my D7800 is repeatedly allocating the same IP Address to the
> same device.

 

   One simple explanation would be that your (unspecified) "the same
device" is repeatedly requesting an IP address from the DHCP server.
I'd expect any reasonable DHCP server to grant "the same IP Address to
the same device" if it keeps asking.

 

   If this behavior is observed for only one client device, then I'd
suspect that device, rather than the DHCP server.

Message 2 of 10
TerryJColes
Luminary

Re: My D7800 shows repeated DHCP Allocations for the Same Device

Sorry.  I should have made this clear.  It's multiple devices.

 

I've also realised that the devices that have been given an IP Address multiple times don't seem to appear in the attached devices list.

 

Is this someone trying to guess my WiFi Pass Phrase?  

Message 3 of 10
antinode
Guru

Re: My D7800 shows repeated DHCP Allocations for the Same Device

> Is this someone trying to guess my WiFi Pass Phrase?

 

   If it's a wireless device, then that would be a plausible
explanation.  Or some legitimate device(s) with bad credentials.

Message 4 of 10
TerryJColes
Luminary

Re: My D7800 shows repeated DHCP Allocations for the Same Device


@antinode wrote:

Or some legitimate device(s) with bad credentials.


It's my EV Charger.

 

Thanks foir your help.

Message 5 of 10
TerryJColes
Luminary

Re: My D7800 shows repeated DHCP Allocations for the Same Device


@TerryJColes wrote:

 

It's my EV Charger.

One final query.  When I checked the charger after this disgnosis its status light was red, signifying a failure.  I power cycled it and the repeated DHCP requests stopped - for a while.  Later I recycled both my router and my extender and the repeated DHCP requests stopped again.

 

The Charger Supplier worked through the problem with me on Saturday and informed me that there had been a brown-out on 4th Jan where the mains voltage had dropped to 178 V (normally 230 V).  That's what had caused the red status light.  He said that he thought the problem ws caused by that and it should be OK.  I last used the charger on 1st Jan.

 

However, the repeated DHCP requests have since recurred.  Is there any config settings in my router that could cause this?  Every other client works fine, but I thought it worth checking.  I get the problem whether I connect the charger to the extender or to the main router, so I'm excluding the extender from my diagnosis.

 

I suspect that the brown-out damaged the charger electronics, although why I'm not sure.  Of course the Supplier's monitoring wouldn't see larger narrow spikes, so the brown-out may have been preceded by a large spike (nothing else failed though).  The Charger is under Warranty, so I want to marshal my facts before I call back.

 

Message 6 of 10
antinode
Guru

Re: My D7800 shows repeated DHCP Allocations for the Same Device

> [...] Is there any config settings in my router that could cause this?
> [...]

 

   I know of none.  Netgear consumer-grade routers generally offer very
little opportunity for the user to customize the DHCP server.  (Address
Reservation and address pool limits are about all.)

 

> [...] I get the problem whether I connect the charger to the extender
> or to the main router, so I'm excluding the extender from my diagnosis.

 

   The DHCP server is in the router; any extender should be a passive
bystander.  Removing the extender might be a reasonable diagnostic step.

 

> I suspect that the brown-out damaged the charger electronics, although
> why I'm not sure. [...]

 

   Many things are possible.  If only one client device exhibits the
problem, then I'd tend to blame that device.  But:

 

> [...] It's multiple devices.


would tend to suggest otherwise.  Bad firmware on the router could
account for problems on multiple devices.


   I know nothing about your (unspecified) "my EV Charger" but I can
imagine that it could be configured with a static IP address (outside
your DHCP pool), which should stop any DHCP activity by it.  Shouldn't
be required, but, again, it might make an interesting experiment.

Message 7 of 10
TerryJColes
Luminary

Re: My D7800 shows repeated DHCP Allocations for the Same Device


@antinode wrote:

> [...] It's multiple devices.


would tend to suggest otherwise.  Bad firmware on the router could
account for problems on multiple devices.


   I know nothing about your (unspecified) "my EV Charger" but I can
imagine that it could be configured with a static IP address (outside
your DHCP pool), which should stop any DHCP activity by it.  Shouldn't
be required, but, again, it might make an interesting experiment.


I was in error when I said on Saturday that it's multiple devices; it was the same device being given different IP Addresses.  I only spotted that the MAC Address was always the same after quite a bit of diagnosis.

 

I was thinking about using a static IP Address.  The charger is made by UK Company Pod-Point and there are no user accessible configuration settings other than being able to log on to the device at first-run to connect to a WiFi AP.  However, I can obviosly use the Router's Address Reservation page to ensure that it always gets the same IP.  I see a number of issues with that at the moment:

 

  1. It won't stop the charger asking for an IP Address so it probably won't stop the repeated messages.
  2. If it works it may cover up a real problem.
  3. I need to use the charger today and don't want to risk disrupting that.
  4. I intend to talk to the Supplier again and therefore don't want to add any complications that might confuse the issue.

Thanks for your ideas.

Message 8 of 10
antinode
Guru

Re: My D7800 shows repeated DHCP Allocations for the Same Device

> I was in error [...]

 

   Ok.

 

> [...] there are no user accessible configuration settings other than
> being able to log on to the device at first-run to connect to a WiFi AP.
> [...]

 

   There might be more, but hidden.  I can also imagine that it really
does require DHCP.  (Knowing nothing opens many possibilities to a
fertile imagination.)

 

> [...] I can obviosly use the Router's Address Reservation page to
> ensure that it always gets the same IP. [...]

 

   Yes, but...

 

   Terminology: A "static" address is configured on the device itself.
What you configure on a (DHCP server on a) router is a reserved dynamic
address, not a static address.  Either one should fix the address of a
device, but some implications are different.

 

> 1. It won't stop the charger asking for an IP Address so it probably
> won't stop the repeated messages.

 

   Right.  Because Address Reservation reserves a _dynamic_ address; it
does not involve using a static address.

 

   But yes, it would be more satisfying to solve the DHCP problem, for
which, apparently, we can blame the charger.  Is there a Pod-Point user
forum?

 

   I may not have any more wisdom, but, if you do learn more, I'd be
interested.

Message 9 of 10
TerryJColes
Luminary

Re: My D7800 shows repeated DHCP Allocations for the Same Device


@antinode wrote:

   But yes, it would be more satisfying to solve the DHCP problem, for
which, apparently, we can blame the charger.  Is there a Pod-Point user
forum?

 

   I may not have any more wisdom, but, if you do learn more, I'd be
interested.


Hmmm.  I thought I'd replied to this.  At the time, the Forum software complained of finding illegal chars in my posting and claimed to have removed them.  I could see no change in the 'fixed' message and so I reposted apparently successfully.  Clearly it was not.

 

Anyway.  Pod-Point do not have a User Forum, presumably because the vast majority of their customers are not particulary tech savvy when it comes to IT etc and also there are no user configurable settings in the charger other than the credentials of the WiFi AP that the device is connected to.

 

I phoned their Technical Support line a few days ago and picked up the discussion that had started on the day that this problem was first diagnosed.  I asked if there had been a recent firmware upgrade (a questions which they never actually answered).  However, the support guy pushed the latest firmware, but that didn't fix the problem.

 

I then sent a copy of the Router Log to them showing the symptoms of the problem and drawing their attention to the fact that if the log was filled with unecessary DHCP Requests it was difficult to spot a real problem.  I'm awaiting their response.  It's now been four days, but two of those have been over this weekend so I might get something back soon.

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