Question Questions about DNS, bridge mode, DHCP...

[Perene]

I have been using my local ISP which connects 2 TP-Link routers, #1 and #2 don't have DHCP enabled. The gateway for my ISP modem, which is a MitraStar GPT-2741GNAC-N2, is this one:

192.168.15.1

So, I usually disable the 2.4 and 5 GHz networks from the ISP modem, and only use the TP-Links. Which assign a random IP for the devices, such as 192.168.15.43.

I might also add the fact that I changed the IPV4 and IPV6 DNS from this ISP, in this case I need to do this from the modem, not manually in all devices (for example, my LG TV does not allow this, last time I checked).

Meaning, if I change everyone to 8.8.8.8, they'll use Google, unless they modify, such as using 1.1.1.1 in my PC.

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But now I am replacing my current ISP with a new one, which uses a different modem: Huawei HG8145V5

It looks like this modem not only does not allow the BRIDGE mode (if I am not mistaken, this also applies to the other ISP), yet there's another catch: you can't modify (apparently) the DNS:

https://forum.huawei.com/enterprise/en/can-t-change-dns-on-huawei-hg8145v5/thread/667244851898499072-667213871523442688

So what do you suggest I do, if the modem's DNS can't be changed? Do I need to enable the DHCP in both TP-Link routers? Because if I do, this is what the TP-Link will display:

Currently, the TP-Links are in "Wireless Router Mode". WAN Interface is configured to Connection Type: DYNAMIC IP.

LAN SETTINGS, for one of them I wrote "192.168.15.50", for the other router, 192.168.15.24, so these are their "gateways".

 

[mv2devnull]

It does sound like you current ISP offers you more than one IP address and you do use two of them for your routers.
Furthermore, each of your routers has its own, distinct "home LAN" and they just seem to have overlapping address ranges (192.168.15.0/24 in both).
Each router hides its home LAN from members of ISP's subnet (including your other router) with NAT (more precisely sNAT, aka masquerade).
That is no different from you having one router (and subnet) and your neighbor having one router (and subnet).

The new ISP seems to give only one IP address and it will be assigned to the "WAN-port" of the router that they provide. I.e. the "modem".
The ISP router probably does sNAT. Their idea is that everything that you link to the router is in "one home LAN" -- yours.


You could disable routing (particularly DHCP service) from your router(s) and use them as APs to extend that LAN to wireless clients.
If you were not happy with the choice of DNS service, then you would override that part of config (that comes from DHCP) in your systems.


You could keep your router as router, connect its WAN-port to ISP's router. Then you have up to three separate subnets:
* LAN A, configured by "ISP modem"
* LAN B, behind #1
* LAN C, behind #2
Your client that connects to #1 would be in LAN B, the #1 would NAT outgoing traffic to LAN A, and ISP router NATs again as packets go out to "beyond the modem".
You would decide the config of B and C at DHCP of #1 and #2, just like now.

In principle, the ISP modem, or ISP devices beyond it could filter traffic. Say block DNS queries to force you use ISP's DNS servers.
It is more likely that the cheap device simply lacks management options.