RT-AC66U B1 - LAN interface acts strangely

[Bill_Stewart]

I have an RT-AC66U B1 and have updated the firmware to ASUSWRT 3.0.0.4.386_40558.

My network configuration is as follows:

(TL-PA7010P are AV1000 powerline adapters)

I have an older RT-ACRH13 that works fine in this configuration.

When I put the RT-AC66U B1 in this configuration (using the same IP configuration as the RT-ACRH13), the LAN interface behaves very strangely: I get a few ping responses while it is booting, but then all pings after that time out.

Oddly, I can ping the LAN interface on the DSL modem, the connected VoIP device interface and other connected interfaces on the network, but not the LAN interface on the RT-AC66U B1. Since the LAN interface on the DSL modem requires the LAN on the RT-AC66U B1 in this configuration, there is no Internet connectivity.

Again: The RT-ACRH13 router I am using in the above configuration works flawlessly and there are no issues -- it's been rock-solid since I've set up the above configuration nearly a year ago. But the RT-AC66U B1 is thus far unusable.

Any ideas on what's going on?

 

[Bill_Stewart]

Update: If I disconnect the WAN interface from the RT-AC66U B1, then I am once again able to ping the LAN interface. Reconnect WAN, and LAN interface stops responding again.

 

[ColinTaylor]

That is not a valid network configuration. I'm amazed it ever worked. My guess is that your gigabit switch had detected the problem and gone into some sort of protection mode.

The only scenario I can think of where that type of interconnection is valid is when using VLANs. Are you using VLANs?

 

[Bill_Stewart]

What specifically is invalid about it, why does it work fine with the RT-ACRH13, and how can I fix it?

 

[OzarkEdge]

What specifically is invalid about it, why does it work fine with the RT-ACRH13, and how can I fix it?

Is the DSL modem a router?

Why do you have a router WAN and LAN both connected to the same switch?

OE

 

[ColinTaylor]

As drawn in your diagram the WAN and LAN ports of the router are connected to the same gigabit switch. A router "routes" between two different networks. So unless each of those ports on your gigabit switch are logically connected to two separate networks (e.g. using VLANs) this is simply not a valid setup.

Was your old RT-ACRH13 configured as a router or an access point?

 

[Bill_Stewart]

DSL is in "transparent bridge" mode (no NAT). Router performs PPPoE and NAT (wireless router mode). There is a gigabit switch on either side of the powerline adapters. That would be layer 2, I thought. It works with the RT-ACRH13...if it's not valid then i would think it wouldn't work at all. Unless I am missing something?

 

[OzarkEdge]

DSL is in "transparent bridge" mode (no NAT). Router performs PPPoE and NAT (wireless router mode). There is a gigabit switch on either side of the powerline adapters. That would be layer 2, I thought. It works with the RT-ACRH13...if it's not valid then i would think it wouldn't work at all. Unless I am missing something?

This is how I'd do it:

ISP <> modem <> router <> switch <> clients

OE

 

[Bill_Stewart]

The reason for the powerline adapter configuration is to position the router in a better location in the house.

The gigabit switches are not smart switches, so the physical network segment switch -- powerline -- powerline -- switch should just be layer 2, unless I am missing something obvious?

 

[ColinTaylor]

DSL is in "transparent bridge" mode (no NAT). Router performs PPPoE and NAT (wireless router mode). There is a gigabit switch on either side of the powerline adapters. That would be layer 2, I thought. It works with the RT-ACRH13...if it's not valid then i would think it wouldn't work at all. Unless I am missing something?

As I said initially, "I'm amazed it ever worked". The only way I can imagine this working is by pure luck as you would have two DHCP servers on the same LAN fighting for control and a conflict in addressing.

 

[OzarkEdge]

The reason for the powerline adapter configuration is to position the router in a better location in the house.

Powerline, cables, switches, etc. are the <interconnects>. Use them but keep them separate from each other. You can't connect the router WAN and LAN together with a cable/switch.

ISP <wire> modem <powerline1> router ...
... <wire> switch <wire> clients
... <powerline2> switch <wire> clients (voip client)

OE

 

[Bill_Stewart]

As I said initially, "I'm amazed it ever worked". The only way I can imagine this working is by pure luck as you would have two DHCP servers on the same LAN fighting for control and a conflict in addressing.

There is only one router (DSL modem is in bridge mode) and one DHCP server (the router). As noted, the network segment shared by the gigabit switches and the powerline network is all layer 2 (unless I am misunderstanding something). The fact that both of the router's interfaces are connected to that segment shouldn't matter (and in fact doesn't matter when using the RT-ACRH13, where, as noted, the configuration works flawlessly).

If what you are saying is correct, it shouldn't work, but yet it does.

So there are two possibilities: 1) It shouldn't work, but It works by accident due to a flaw in the RT-ACRH13, or 2) it should work, but it doesn't due to a problem in the RT-AC66U B1.

In the case of #1, I have a happy accident, but left unexplained is why it works.

In the case of #2, what's wrong with the Rt-AC66U B1 that prevents this from working?

 

[ColinTaylor]

There is only one router (DSL modem is in bridge mode) and one DHCP server (the router).

Sorry, my mistake. I forgot you're using a PPPoE tunnel.

I think I might have an idea what's happening. Try this as an experiment: Log into the router and got to WAN > Internet Connection. Set the "MAC Address" to something that's valid but definitely doesn't exist anywhere on your network (for example click the MAC Clone button and change the last three octets). Apply that change and reboot the router for good measure. Does your network now work as before?

 

[Bill_Stewart]

I will give that a try; thanks. What's your idea about what might be happening?

 

[ColinTaylor]

The Broadcom SoC routers (like the RT-AC66U B1) have what I regard as a rather strange default setup. That is the MAC address of the WAN port is the same as the MAC address of the LAN bridge. I can see why that is (all ports are physically part of the same switch chip) but it's "just wrong" in my eyes. So in your case you are plugging two different interfaces into your gigabit switch that have the same MAC address! By using the MAC Clone option you are making them have different MAC addresses (as it should be IMHO). Anyway, that's my current theory.

 

[Bill_Stewart]

The Broadcom SoC routers (like the RT-AC66U B1) have what I regard as a rather strange default setup. That is the MAC address of the WAN port is the same as the MAC address of the LAN bridge. I can see why that is (all ports are physically part of the same switch chip) but it's "just wrong" in my eyes. So in your case you are plugging two different interfaces into your gigabit switch that have the same MAC address! By using the MAC Clone option you are making them have different MAC addresses (as it should be IMHO). Anyway, that's my current theory.

That's interesting. Thanks for the info. Before I'm able to test this I'm going to find out if the Qualcomm-based RT-ACRH13 has the same default.

 

[noah way]

Noob here, but it seems to me that putting the router before the switch would be the logical configuration.

Nice ASCII plan.

 

[Bill_Stewart]

Noob here, but it seems to me that putting the router before the switch would be the logical configuration.

The reason for this design is to place the router in a more advantageous spot to maximize its signal. Moving the router to location of the DSL modem greatly attenuates the WiFi signal (particularly the 5GHz band).

 

[noah way]

At the bottom of your diagram go from link > switch > router TO link > router > switch.

 

[Bill_Stewart]

At the bottom of your diagram go from link > switch > router TO link > router > switch.

That won't work because then there's no connection back to the DSL modem. (Remember, there are two interfaces on the router.)