Problem with Repeater Mode

[fonix232]

So, the situation is quite sticky.

My landlord replaced the main router with a ZyXEL Armor Z1, and set up (drum roll please) MAC filtering.

Luckily for some reason, on the 5GHz network, every device can bypass the filter. shirtty soft filtering from ZyXEL...

So I purchased an RT-AC66U B1 to create a repeated network, basically using it as a Layer 2 device.

Initially it worked fine, everything went through neat, but I wasn't able to access the router web UI. To fix this, I contacted Asus support, who suggested resetting the router and setting it up again.

I did so, and in the meantime switched to AsusWRT-Merlin, version 380.65 - the release from today.

And ever since, even after going back to the official firmware, I'm unable to get DHCP pass-through working. It simply does not happen.

Router is in repeater mode, with fixed IP, gateway and DNS address (gateway/host router is 192.168.10.10, my router is set up as 192.168.10.70, SSH and web GUI allowed on both WAN and LAN, DNS is set to 8.8.8.8, 8.8.4.4).

Is this a known issue? Or am I running into something new?

 

[RMerlin]

Without knowing how the upstream router is configured, it's impossible to determine what is going on.

 

[fonix232]

The upstream router (host router) is configured as a simple wireless AP, 192.168.10.0/24, with it being assigned the address 192.168.10.10.

Unfortunately I do not have access to the config panel of the router, so I can't say much more. The thing is, it did work before, and the same settings now do not.

 

[fonix232]

But the most interesting thing is that a day ago DHCP passthrough worked without an issue, with the very same configuration. And I don't think that your firmware leaves any remaining bits around when a stock firmware is flashed and NVRAM is erased.

 

[fonix232]

Okay it seems like I've made some progress...

After restoring stock firmware by erasing NVRAM both before and after flashing, I was able to set up repeater mode with DHCP passthrough (or forwarder, I'm not sure how Asus solved it).

So with stock firmware it works fine.

After that, installing 380.65 instantly kills DHCP, and for some reason if a device happens to receive a DHCP address, it is from the repeater, not the host router (subnet matches, but device does not appear on host network, does not have internet access, and gateway is set to be the repeater's local IP).

I'll try with some older versions, see if the latest 380_4180 merge caused the issue, or something else.

 

[prestonwho]

Hey -

Similar situation (I think). I do have access to my main router's config but I don't think that's the issue.

Main router (a crappy model rented from Comcast): 10.0.0.1
Second router (Asus ac66u running Merlin's 380.67): 10.0.0.2

For a while I couldn't figure out why systems connected to the repeater's Wifi could talk to each other but not the Internet. I dug in the settings and found that the Asus repeater was giving the default gateway of 10.0.0.2 (itself) instead of the network's real default gw of 10.0.0.1.

I need the repeater either to provide 10.0.0.1 as the default gateway to DHCP clients, or to forward packets received on 10.0.0.2 to the real gw at 10.0.0.1. I'm not sure how to do either on the Asus router. I've poked around via SSH a fair amount, but I don't see where this would be configured.

Anyone have any helpful thoughts?

 

[ColinTaylor]

For a while I couldn't figure out why systems connected to the repeater's Wifi could talk to each other but not the Internet. I dug in the settings and found that the Asus repeater was giving the default gateway of 10.0.0.2 (itself) instead of the network's real default gw of 10.0.0.1.

I need the repeater either to provide 10.0.0.1 as the default gateway to DHCP clients, or to forward packets received on 10.0.0.2 to the real gw at 10.0.0.1. I'm not sure how to do either on the Asus router. I've poked around via SSH a fair amount, but I don't see where this would be configured.

Are you actually in repeater mode? It doesn't sound like it because the repeater shouldn't be doing DHCP or giving out gateway information. All it should doing is receiving wireless data from the clients and sending it on wirelessly (repeating it) to the main wireless router.

 

[prestonwho]

Are you actually in repeater mode? It doesn't sound like it because the repeater shouldn't be doing DHCP or giving out gateway information. All it should doing is receiving wireless data from the clients and sending it on wirelessly (repeating it) to the main wireless router.

It's in repeater mode, at least according to the Web interface and the fact that the addresses given to the hosts connecting to it are on the same subnet as the main router. You're probably right that the DHCP addresses are being assigned by the primary router, because devices connecting to the repeater are getting the same IP addresses that they got when they were connecting directly to the primary. So it appears that the repeater is forwarding the DHCP requests. However... I can't figure out why the devices that get their addresses via DHCP are getting 10.0.0.2 (the repeater's IP, not the primary) as their default gateway.

So... anybody with a little more networking background than myself have any guesses why the devices would be getting the repeater's IP as their default gateway? The primary router is far less configurable than the Asus repeater, and certainly doesn't have any setting for what default gateway to provide to DHCP requests forwarded by a repeater.

 

[ColinTaylor]

@prestonwho If it is some sort of bug in recent firmwares I would try flashing the oldest firmware the router will take, 380.61 and see if that fixes it.

EDIT: Another thing you could do to investigate is to log onto the repeater and see if dnsmasq (the DHCP server) is still running. I don't know for sure, but I'd expect it not to be. In which case the following command should not return anything:

admin@RT-AC68U:/# ps w | grep dns | grep -v grep
 3882 nobody    3132 S    dnsmasq --log-async

 

[prestonwho]

@prestonwho If it is some sort of bug in recent firmwares I would try flashing the oldest firmware the router will take, 380.61 and see if that fixes it.

EDIT: Another thing you could do to investigate is to log onto the repeater and see if dnsmasq (the DHCP server) is still running. I don't know for sure, but I'd expect it not to be. In which case the following command should not return anything:

admin@RT-AC68U:/# ps w | grep dns | grep -v grep
 3882 nobody    3132 S    dnsmasq --log-async

So... the dnsmasq process is running. For giggles I killed it, and it stayed dead for less than 5 seconds before restarting itself. I'll look into what's restarting it, but if anyone has any insights, please join in.

I'll try installing an old firmware when I have a sec.

 

[ColinTaylor]

So... the dnsmasq process is running. For giggles I killed it, and it stayed dead for less than 5 seconds before restarting itself. I'll look into what's restarting it, but if anyone has any insights, please join in.

After I posted that I looked at an access point configuration (I don't have a repeater available) and I think that dnsmasq probably will be running, but the DHCP server will be disabled in the config file. You probably won't be able to kill the process because there's a task that restarts system services. Can you post the output of /etc/dnsmasq.conf please.

 

[prestonwho]

admin@RT-AC66U-09A0:/tmp/home/root# cat /etc/dnsmasq.conf
pid-file=/var/run/dnsmasq.pid
user=nobody
bind-dynamic
interface=br0
resolv-file=/tmp/resolv.conf
servers-file=/tmp/resolv.dnsmasq
no-poll
no-negcache
cache-size=1500
min-port=4096
no-dhcp-interface=br0
admin@RT-AC66U-09A0:/tmp/home/root#

 

[ColinTaylor]

no-dhcp-interface=br0

OK. So DHCP isn't running on the repeater, which is good.

So I think you're back to trying to flash an older version of the firmware.