G3100 DHCP Assignment Problem
kalyish
Enthusiast - Level 2

Got the G3100 a few months ago, upgraded from an ancient ActionTec.  Had to make some tweaks to the configuration:

- Disabled SON

- Separated the 2.4GHz and 5GHz networks into separate SSIDs

Those tweaks solved some issues I was having.  But one issue is still occurring.  I first noticed it with my Roku Streaming Stick Plus where I would turn it on, but it wouldn't have any internet connectivity.  Tried many, many things but the only thing that would work is rebooting the router.  I later discovered that I didn't even have to reboot it - just turning off the 2.4GHz and then turning it back on would be enough to allow the Roku to connect.

So all of a sudden the Roku isn't having any problems and everything is fine for a few days, but now the wireless printer can't connect.  Same thing - turn off 2.4GHz, restart it, and everything is fine.

I checked out the DHCP LAN log on the G3100 while troubleshooting both problems and one thing I noticed was a DHCPDISCOVER/DHCPOFFER loop whenever the problem was happening.  Restarting the 2.4GHz networking cured the loop and I then saw the expected DHCPREQUEST and DHCPACK entries in the log.

I have now set up my printer with a static IP address, both on the printer itself and in the G3100 network settings.  The Roku is still getting its address via DHCP, but I have it set up as static on the G3100.

It seems that the DHCP loop might be a clue, but I don't understand enough to figure out why restarting the network would clear it up or how to fix it.

I have Hardware version 1104 of the G3100 and Firmware version 1.5.0.10

The G3100 is the only router on my network.

Every other networked device on my LAN is a client.

There are only 20 clients.

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Cang_Household
Community Leader
Community Leader

G3100 is very strict about device name (or NetBIOS name) when renewing the DHCP lease. If your device names have special characters (except dashes and underscores) in them, G3100 would refuse to renew the IP address. I guess, technically, having special characters (including spacebars) in the device name is against the standards set forth by IETF, specifically RFC 952.

For a static IP address, you should configure the address on the devices. The static addressing on G3100 is for static DHCP assignment, meaning every time the G3100 will renew/re-lease the device with the same IP. A static IP address on the device, however, abandons the request/renew/re-lease processes entirely.

kalyish
Enthusiast - Level 2

Thanks for your reply, Cang_Household.  I forgot to include in my original post that I had seen the earlier discussion on this forum about forbidden characters in the device name.  I actually dug out an old phone yesterday to change its name because it had a space in it.  Then when I went to Advanced/IPv4 Address Distribution/Connection List, there weren't any devices with forbidden characters in their names - just letters and dashes.

It doesn't seem like my G3100 is having an overall problem with lease renewals though.  Most of my devices are working fine.  But the Roku had issues for weeks, and the printer started yesterday.  And the DHCPOFFER entries in the log seem to indicate that the router is *trying* to give out the address, but there's no subsequent DHCPREQUEST from the printer followed by the DHCPACK from the router.  So I'm not so sure that my scenario matches the one described in the post about device names with forbidden characters.  I did just change the name of the old phone yesterday, though, so maybe there's some kind of table in the router that I can't see that will eventually get flushed.  Thanks again for the response!

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Cang_Household
Community Leader
Community Leader

Do the issues emerge from a firmware update on either the device or the router?

kalyish
Enthusiast - Level 2

I had previously checked all the firmware for updates, but I after your suggestion I double-checked in case I had missed something.

G3100 - Can't tell when it was updated

Roku - Was updated in August, has the latest firmware

HP Printer - Firmware updated 2 weeks ago (!)

Did a little more research on the printer and changed one setting, which is now allowing it to connect to the network via DHCP.  In case anyone else encounters this issue, I checked the box on the printer's network settings for "In an infrastructure network use 802.11b/g behavior options."  I'll see if this solves the issue, but since rebooting the router also solved the issue temporarily, I need to wait a bit to see if the problem resurfaces.  But I'm hopeful that this is the solution, so thanks for the suggestion to look into the firmware.

Cang_Household
Community Leader
Community Leader

If you go to G3100's System logs. The rebooting event is a pretty good sign of firmware update. I am not sure what is the exact log message though.

Choosing 802.11b/g? That is using archaic wireless protocols. I guess they work because not so much data is transmitted for printing. If you can hardwire the printer, definitely hardwire it and disable its WiFi/Direct/Bluetooth altogether, so nobody can hack your printer and waste the expensive ink.

kalyish
Enthusiast - Level 2

Regarding 802.11b/g - absolutely archaic.  It's definitely a workaround solution.

Regarding the system logs - also archaic.  No filters, no downloading, only scrolling through page after page of entries.  But good point about the rebooting event as a sign of an update.

kalyish
Enthusiast - Level 2

Back to the DISCOVER/OFFER loop on the printer so 802.11b/g did not work.  I can just set up a static IP on the printer or connect it to the router via an ethernet cable as was suggested, but it doesn't answer the question of why it happened on the Roku and now the printer.

kalyish
Enthusiast - Level 2

DHCPDISCOVER/DHCPOFFER loop now occurring on my kid's tablet.  Unfortunately, I know just enough about DHCP to know that this isn't right, but not enough to determine the root cause.

Has anyone else noticed these loops in their LAN DHCP Logs?

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Cang_Household
Community Leader
Community Leader

Can you use WireShark to capture the DHCP exchange process? I want to see the entire Discover-Offer-Request-Acknowledge cycle. It’s possible that G3100’s DHCP server glitches. It seems like the clients cannot get the DHCP Offer packet for some reason.

kalyish
Enthusiast - Level 2

I've never used WireShark but I'll download it and figure it out.  Thanks for pointing me in the direction of something that can capture the traffic.

I also looked at the tablet, which hasn't been used in a while - spaces AND an apostrophe in the device name.  I don't know if that was the problem, but I changed the device name on the tablet anyway.

Off to figure out WireShark - thank you!

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Cang_Household
Community Leader
Community Leader

Regarding the device name containing special characters other than dashes and underscores, it is unacceptable per RFC 952.

Once a client send DISCOVER broadcast, the DHCP server should reply with an OFFER unicast. Then the client should send a REQUEST broadcast, the DHCP server should reply with an ACKNOLWEDGEMENT unicast. It seems to me either the client has never received the OFFER unicast or it fails to REQUEST the DHCP server.

kalyish
Enthusiast - Level 2

The tablet is a Fire Tablet and it turns out that the device name which I edited is the one by which Amazon identifies it.  It's not the same one that is sent out on the network, so the apostrophe and space were irrelevant.

But I've experienced this DISCOVER/OFFER loop with three different devices now.  The only difference in my network since this problem began is replacement of the old Actiontec router with the G3100.  I would be interested to hear if others have noticed the same loop in their router logs.  In the meantime, I'm monitoring with Wireshark so I can have more data.  Thanks for the responses, and thanks for suggesting Wireshark!

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hvrf
Enthusiast - Level 2

One possible idea: I've read that the G3100 is limited to 10 static dhcp addresses for some ungodly reason, and without any error statement. Is it possible that when you add one, it bumps a prior one off the 10, etc.? Would account for why it involves multiple devices.

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Cang_Household
Community Leader
Community Leader

Why would you need that many static DHCP assignments?

I rarely see devices those require a DHCP query in order to obtain an IP address. You always seem to have the option to assign a static IP at the device.

Static IP Assignment and Static DHCP Assignment is different. They are not interchangeable terms. Static IP Assignment requires you to configure the IP address directly onto the device. Whereas Static DHCP Assignment is configured on the DHCP server, namely in this case, the router.

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hvrf
Enthusiast - Level 2

I know this has been discussed in other threads, with general disagreement about whether it's better for a device to specify its own static IP address, vs. having the router distribute a static IP address (DHCP) to each. Personally, I'd prefer to have all the static assignments done from one list, i.e., the router, rather than go to each device. In my own home we have approaching 40 devices with IP addresses. I also understand some devices like home automation and security may desire static IP addresses without their own ability to specify one, although I don't have those.

In any case, no other router I've had had such a limited pool available. I see people mentioning this over a year ago, and hoping for a firmware update, but as far as I know it hasn't been addressed yet (here's hoping).

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Cang_Household
Community Leader
Community Leader

At home, I have 36 devices that are statically assigned an IP address. I don't see this as a hassle because I need to change each device's configuration anyway for security.

IoTs (security cameras, smart light bulbs, smart plugs, and etc.) lacking static IP assignment capability are not "smart." Smart devices should not be one size fit all. I know some may want Plug and Play, but it compromises security inevitably.

When you have all static assignments "done from one list," you are essentially create a pivot point on your network. If the router goes down or get hacked, all DHCP devices will go down with it. You already have lots of pivot points in a home network, so don't create more single-point-of-failure.

G3100's DHCP server is limited. Besides waiting for the engineering to mend this issue, you can take this issue into your own hands and configure your own DHCP server. Once you got your own DHCP server, you can have complete control over your network's DHCP assignments and reservations. You can even set your own rules.