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I have a brand new Asus ZenWiFI XT8 mesh system set up and working ... for the most part!

My main PC has 2 interfaces: Ethernet & WiFi. WiFi is connected and gets an IP from the router. The Ethernet connection, however does not get an IP!

When I run WireShark (while running ipconfig /renew Ethernet), I see plenty of unanswered DHCP Discover messages. If I run ipconfig /renew Wi-Fi though I see the DHCP Offer and ACK messages almost immediately and boom! WiFi is connected.

I have:

  • Changed Ethernet Cables
  • Tested my Ethernet Cable with a cable tester
  • Bypassed my switch and gone directly to the router
  • Rebooted into Linux and tried renewing IP
  • Tested with a Raspberry Pi and tried getting an IP
  • Re-installed Windows
  • Tried to set a static IP (in Network configuration)
  • Tried to set a DHCP reservation for my NIC

What's interesting is the adding my NIC's MAC address to the DHCP reservation list has no effect. It does NOT get added to the list. Now this package comes with a pair of routers. None of the devices plugged in to the wired ports shows up in the client lists.

I'm all out of ideas ... WTH is going on? Obviously the DHCP server is working. There are 17 clients connected wirelessly without any issues (including this PC), but those same devices cannot connect through the wired connection (including this PC).

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  • Seems like your router has a bug.
    – Spiff
    Commented Apr 23, 2020 at 7:08
  • When you can (if there are plenty of other users connected at the moment, you might want to warn them in advance...), turn WiFi off in the router, and see if you can get an IP with only your PC connected via Ethernet. If yes, then there may be a limit to the number of devices the router can cater simultaneously, via WiFi AND Ethernet, and maybe you've reached that limit wihout knowing it. If not, well, as Spiff said, your router got off its rocker and needs to be reset. That too should be done when other users aren't around, or prepare the earplugs...
    – user1019780
    Commented Apr 23, 2020 at 7:36

2 Answers 2

Reset to default
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Try setting 100Mbps full duplex in network card settings "Network and sharing center" -> "Change adapter settings" -> "Properties" on LAN connections -> "configure" button -> "advanced" tab -> "Speed and duplex" set to "100Mbps full duplex"

Looks like gigabit uplink issue.

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So after checking the switch for loops and not finding any, I took everything off the switch (only 4/8 ports), disconnected the switch, and connected the PC directly to the router. DHCP renew worked right away. I connected the same devices as before to the switch one by one and tried DHCP renew after each one, still watching WireShark making sure there no unanswered DHCP Discover packets. Things work now even though there's no difference between now and before. I remember checking the switch for loops multiple times and not finding any, but maybe there was something at some point and the router blacklisted the switch or something.

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    Many low-end switches have limited mac-address lookup table space. And often not so very good garbage collection on those tables. This leads to the tables getting clogged up over time with the sort of weird effect you noticed. Rebooting the switch will usually clear those tables and everything works again. I've seen routers with the same problem on their internal switch as well. It almost looks as if you had that sort of problem with your switch.
    – Tonny
    Commented Apr 24, 2020 at 14:02

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