Monitoring bandwidth with luci-app-nlbwmon and two routers on the same subnet

Hi dear network experts!

Can you please help me understand if this scenario is viable?

I have a network with a modem/router set up with my ISP's software and all. This has not been modified. On top of that, I have a TP-Link TL-WDR4300 v1 with OpenWRT installed and cabled onto the main modem/router. They are both on the same network, I have set the openwrt router as the DHCP server and so have set it as the gateway for all the devices. I did this basically because the ISP modem/router wouldn't let me set the DNS and I was able to customize it through the dhcp options. The openwrt router itself has the ISP modem/router as the main interface gateway.

Since I already had all the devices connecting to the openwrt router as the main gateway, I thought I'd try to add some bandwidth monitoring just for fun.. I have installed luci-app-nlbwmon in the openwrt router, and I can see it is able to capture what seems to be the amount of connections flowing through it, but it seems unable to provide me with the amount of data that is transferred from/to the devices. I can see only the amount of data that the router itself transmits/donwloads, when I SSH into the router and do some downloads. For example:

Is this some configuration I am missing? The luci-app-nlbwmon config is basically from factory. I have only one network to monitor which is the "lan-br" one, and a couple of interfaces for the WLAN bridges on the openwrt route.

I thought this could be because that perhaps because both the modem/router and openwrt router an in the same network, the devices are simply bypassing the openwrt router when reaching the internet. It doesn't make much sense to me though if this is the case and to have this presented on the traceroute for some random internet domain:

Guilhermes-MacBook-Pro:~ pimguilherme$ traceroute
traceroute to (, 64 hops max, 52 byte packets
 1  * (  2.258 ms  1.450 ms        <<<<<< openwrt router
 2 (  1.514 ms  1.738 ms  1.587 ms <<<<<<<< ISP router
 3 (  8.540 ms  6.437 ms  47.248 ms
 4 (  4.372 ms (  4.711 ms (  3.783 ms
 5 (  3.815 ms (  4.577 ms (  4.360 ms
 6 (  119.200 ms

Can you please help me understand how to achieve bandwidth monitoring with this setup? Would I need to separate the networks from both routers?

Added question: this would bring me to another topic which is a bit weird.. the cabling from the ISP modem/router to the openwrt router initially only provided me with 100Mbps initially, even though the ports and the cables should be Gigabit after a lot of research I did.. and then when I did some unrelated configuration on the main ISP modem/router and reset it, for some reason the link got up to 1GBps.. That remained for a few weeks and now I checked it again and it's back at 100 Mbps.. any ideas?

Thanks much in advance for your time and help!

All the best :slight_smile:

This, at least if I understand you correctly, cannot work. Routing works by forwarding packets from one subnet to another, therefore the subnets (IP address ranges) must differ between WAN and LAN.

If I understand you correctly, all of your clients are in the same subnet as the ISP router and your tl-wdr4300, which means routing doesn't take place and most traffic bypasses your tl-wdr4300.

All the cable/fiber modem/routers I've worked with have a bridge mode where you can transfer the routing duty over to an OpenWRT device. That's complicated of course when for example in cases like where a telco has an ATA (VOIP setup) internal to the modem as well, and in that case (to preserve the function of the ATA or local "landline") I've pleaded with some ISPs and they set up an additional virtual PPPoE port off one of the LAN ports which did the duty by allowing me to configure PPPoE from an OpenWRT router with the WAN attached to their designated LAN port of their modem/ATA/router and then I used that OpenWRT router as the only access point and simply didn't publish for use the password to the ISP furnished modem/ATA/router.. One problem is in bridge mode and if you are dealing with a fiber modem where PPPoE is used, the PPPoE password may be hidden from the stock modem/router configuration setup link and you have to convince ISP support you need it. Otherwise sometimes it can be extracted by using the browser Inspect Elements elements and changing the field type from password to text..

Thank you guys! They are indeed on the same subnet and I am not sure I would change that to have this feature because anyway some of them would connect directly to the main modem due to wifi areas and would skip the bandwidth monitoring anyway.. And it has been very easy an d helpful to have all of them in the same network all the time :slight_smile:

I will try to look for the routing transfer option in the modem, thank for that suggestion! I might not go with it because the link between the modem and the openwrt router for some reason drops to 100mbps instead of 1gbps.. Would anyone have any hint on that? It really looks like nothing has change physically, but the link drops speed.. I find it a bit hard to think it's due to the cable because I did some tests locally with other cables and they behaved the same way on the modem/router, so perhaps it could have some thing to do with its port or config..