How to access modem that is in bridge mode from a router connected to it?

[vacatedzeus2]

TP-Link Archer AC2600/A10

 

[WandereR]

If your LAN and WAN is not properly isolated (in firmware), this can result in DHCP leaking out IP addresses on LAN, hence is discouraged.
(Happens more often than you might guess, specially in bridge mode on cheap ONUs.)

Can you please explain this ? I didn't quite get it.
My config:

 

[armaan_99]

I think this can be achieved in TP-Link Routers only, any one achieved this in a Tenda or a D-Link routers.

 

[WandereR]

@armaan_99 Mine is D-Link and I can access ONU's page while being connected to the router. Check the screenshot in the post before yours.

 

[drtech]

Can you please explain this ? I didn't quite get it.

For this, you need to understand that bridge mode is not exactly like how a dumb switch would behave. Bridge mode infact is selective repeater that allows only certain protocols to traverse on either side of the two interfaces it is bridging. So to say, for example, it acts as a PPPoE relay, rather than just forwarding the packets between interfaces.

In properly implemented firmwares, a DHCP server acting on the LAN side should not leak IP address to the WAN side, thus preventing every other person on the same fiber network to start getting an IP address in your LAN subnet offered by the DHCP server. But, in half baked firmwares, this block is not properly executed, and hence all other devices on the same fiber line start acting as a client to your LAN DHCP server (not necessarily a bad idea, however if you are even little bit concerned about your security, this is a disaster).

So the best practice is to change the default management IP of your ONU to something a little non standard, and then completely disable DHCP on LAN. Then configure a static IP on your secondary connection manually.

 

[WandereR]

@drtech Do you mean to say, I should change my ONU's IP from 192.168.1.1 to something other like 192.168.50.1 ? And then change the subnet accordingly and finally setup the same in my router as static ?

 

[armaan_99]

@WandereR Your ONU is not in Bridge mode, can you confirm if you can access modem when it’s in Bridge mode via router.

 

[drtech]

I should change my ONU's IP from 192.168.1.1 to something other like 192.168.50.1

Yes.

 

[crazyuploader]

@drtech It worked like charm man! I was trying 192.168.1.1 and it did not work, then just as my last guess, I also tried 192.168.100.1 and it worked! Seems like my ISP might have changed its IP, though I am getting wrong credentials for ONT's web interface and the password which is written under the ONT doesn't work

 

[WandereR]

@WandereR Your ONU is not in Bridge mode, can you confirm if you can access modem when it’s in Bridge mode via router.

It was in bridge mode. The PPPoE was not configured for my ONU. And yes I can access modem(ONU) when it's in bridge mode. Check the screenshot in my previous message: There was a dynamic IPv4 assigned to my router(through my ONU).