Duplicate IP Address

Guru

Mar 19, 2020

> [...] I can't help but wonder, however, that the router gave two
> different devices the same IP. [...]

The _router_ (strictly, the DHCP server in the router) should not
grant the same IP address to two different devices. But, if _you_
"manually" assign a static address to some device, then that device uses
that address, without bothering to ask the DHCP server about anything.
Then, in its ignorance, the DHCP server wouldn't hesitate in granting
that in-pool address to some other device.

> [...] Here's something I may try [...]

If you configure the printer to use DHCP, then it should get its
(unique) IP address using DHCP, like all your other DCHP-client devices.
If you don't explictitly reserve a dynamic address for a device, then
that will come from the DHCP pool (whichever range you specify for
that).

> [...] I would assume they all should...starting at .100. Before I do
> so, does this soound feasible.

Sure. What could go wrong?

If you use Address Reservation to reserve a particular address for a
DCHP-client device, then that device should get that reserved address,
rather than some unpredictable address from the DHCP pool.

If you do use Address Reservation, then my advice is to choose only
non-pool addresses for those reserved addresses. (Just the same as for
any static addresses.) In principle, the DHCP server should be smart
enough not to consider granting an in-pool reserved address to the wrong
device just because it's still (apparently) in the pool, but why trust
it? If your reserved addresses are all ex-pool, then the question
should never arise.

antinode
Guru
Mar 20, 2020
> Okay...I didn't change the DHCP pool range [...]

> [...] so I should be good.

   You now know how to do it right, so that the problem cannot recur,
and how to do it wrong, so that the problem is less likely to recur.
And you picked which of those? Yow.

   Possibly helpful: Web search for the following terms:

      lead horse water horticulture
stepheat
Aspirant
Mar 20, 2020
"Possibly helpful: Web search for the following terms:
lead horse water horticulture"

Good one! I went back in and put a .100 limit on the router and changed my printer to .110.
antinode
Guru
Mar 20, 2020
> [...] I went back in and put a .100 limit on the router and changed my
> printer to .110.

   "limit"? Everything's a limit. Which value did you change?

   "changed my printer"? You're still configuring your printer with a
static address (configured on the printer), not reserving a dynamic
address for the printer on the router, and configuring your printer to
use DHCP?

   As usual, many things are possible. Some of them even work reliably.
stepheat
Aspirant
Mar 21, 2020
Under LAN Setup the "Use Router as DHCP server" is checked. The starting IP address is 192.168.1.2 . I changed the ending IP address to 192.168.1.100 so my printer at .110 is outside the range.
antinode
Guru
Mar 21, 2020
> Under LAN Setup [...]

Sounds reasonable. So long as you have some non-pool addresses,
like, say, ".101" - ".254", you should be able to use those as reserved
dynamic or static addresses. What could go wrong?

> [...] ending IP address to 192.168.1.100 [...]

Some people might have chosen ".99" there, so that _any_ ".1xx" (or
".2xx") value would be easy to recognize as non-pool.
Technowizard
Tutor
Mar 21, 2020
I wouldn't say this issue is "solved" by no mean. I've had this router for over a year, and I'm pretty familiar with its advanced configuration settings. That said, I too started getting duplicate assigned IP addresses on my network immediately after updating. I have just over 80 devices on my network (smart home), and at least 3 or 4 keep getting duplicated with no rhyme or reason - sometimes it'll be a duplicate between my 5GHz & 2.4GHz devices, sometimes between the router and my AP unit, and then sometimes duped solely on the router's 2.4Ghz band. I've tried soft/hard rebooting, disconnecting power for 30+ minutes, manually reloading firmware, clearing and reloading configurations, changing router/AP boot order, etc; all with no help. Downgraded it back to v1.4.1.42, and everything again works as well as it used it.

I probably won't check back in on this, as I'm not staying on this setup much longer... it just can't handle the demands I'm asking of it anymore, so I'm moving on up to a Unifi HD setup. I just wanted to comment here to report that v1.4.1.50 randomly breaks IP assignment protocols. I'd suggest just downgrading to v1.4.1.42 until Netgears figures things out (if they even attempt it), though that version had it's own issues (on occassion drops WiFi settings to factory default, as well as refusing to update the connected devices list 90% of the time).
antinode
Guru
Mar 22, 2020
> I wouldn't say this issue is "solved" by no mean. I've had this
> router for over a year, [...]

   "this issue"? "this router"?:

> Model: R6100|AC1200 Dual Band Router

   Or "this router"?:

> Model: R7900P|Nighthawk X6S AC3000 Tri Band WiFi Router

   Different hardware, different firmware, different environment? All
good reasons to start a new thread, instead of diverting this one.

   Unless I missed something, this thread dealt with a printer having a
static address which was still in the DHCP pool. I see no particular
reason to believe that your problem is similar, unless you also assign
static IP addresses from your DHCP pool. There's more than one way to
get address conflicts with DHCP, most notably, having two active,
uncoordinated DHCP servers.
Technowizard
Tutor
Mar 23, 2020
Yeah saw later on that this was for a different router, but couldn't delete or modify my post for some odd reason. Wasn't trying to divert anything... just searched for "R7900P duplicate IP," and this one came up and had a creation date that matched when the firmware came out. My problem is unrelated to static IP and DHCP IP reserving, as I believe it to be purely a firmware bug.

Forum Discussion