Why do some devices not show up in the connected clients list on my Asus RT-AC68U router?

I have two other routers (RT-AC57U) connected to my main router via 30m ethernet cables, and set up as access points.

Everything works perfectly - I can connect via wifi to any of the routers, and access the internet fine. I have them set up as 192.168.1.1, 192.168.1.2 and 192.168.1.3. I have DCHP on the main router set to only assign IPs from 192.168.1.100 and upwards.

I can connect via a web browser to the interface of any of the routers, regardless of which one I'm connected to.

So it all "works".

The one thing that doesn't, is 99% of the time the two 57 units don't show up in the connected clients list on the 68. Very occasionally they DO, but most of the time they don't.

Any idea why, and what I could change so they always showed?

Thank you

3 Answers

Routers don't actually know what devices are connected – there is no mandatory "attach procedure" on Ethernet IP networks. (Indeed DHCP is probably the closest you can get.)

Because of that, if the router wants to show you a device list for information, it has to build it based on various activity it sees. And that mostly comes from these sources:

1. Address lease table, based on DHCP requests.

2. ARP cache, based on packets sent to / received from the device's MAC/IP addresses.

The first source clearly doesn't apply because the units are not DHCP clients. But importantly, the second source (ARP cache) also doesn't apply – because your extra units act as access points (i.e. they're bridges), they almost never generate any packets from their own IP or MAC addresses! They just transparently relay packets from your various client devices.

Additionally, traffic that's within the same subnet (e.g. from a local PC to the access point's web admin UI) won't update the gateway's ARP cache either, because it doesn't go through a gateway by definition.

So the only time a bridge will show up in a router's ARP cache is when it generates some traffic to the internet, e.g. when it checks for firmware updates, or when it syncs its clock against an NTP server. Your RT-AC57U units probably have a "ping/traceroute" admin page – use it to test this theory.

what I could change so they always showed?

Consider adding DHCP "reservations" aka "static leases" for those access points. That might be enough on its own, or you might need to actually make them act as DHCP clients (but that way they'll still get the same .2 and .3 addresses every time).

Since the router supplies the IP address to whatever is connected to it or through it ("through" meaning connected via repeater), and since it is its DHCP server that allocates the addresses, it will know about all connected devices, their IP and MAC address.

However, I believe that in your case you have given the two repeaters static IP addresses, so they have no need to connect to the main router. They will just pass on connections for their connected devices.

The main router should still be able to detect such communication. If it doesn't, then this part of the firmware is not updating the attached devices list for that case. The DHCP server code in the router seems to be doing a better job.

This shouldn't be worrisome, as everything "just works". The most you can do is ensure that all firmwares are up to date (which you should do anyway as a security measure).

I have RT-AC66U B1, ( Firmware Version:3.0.0.4.386_40558 ) I resolved the missing network clients in the client list by enabling a guest network.

With no guest network enabled, all clients connect and function on the network but for some reason the list can only display 10 clients. I enabled a guest 2.4ghz SSID and then all clients showed up, wired and both wireless frequencies.