How to access modem from router when modem is in the bridge mode?

piotr_dobrogost
Aspirant
Mar 23, 2021
antinode wrote:
https://community.netgear.com/t5/x/x/m-p/2066232

> [...] it should be possible to access modem's web UI from LAN when
> modem - connected to the router - is in bridge mode. [...]

Says who? It depends on the modem. If not, then it's not a router
problem.
It's true modem has to support it in bridge mode and this modem does support it which I checked by connecting computer directly to one of modem's LAN ports, obtained IP 192.168.1.4 and accessed modem's web UI at IP 192.168.1.1
Now I'm concerned with what is needed on the router side to access this modem. As shown in the answer cited they had to properly configure router so hosts on the LAN could access modem through it. I'm asking about how to configure R8000 using original firmawe the same way they configured their router using DD-WRT.
- antinode
  Guru
  Mar 24, 2021
  > It's true modem has to support it in bridge mode and this modem does
  > support it which I checked by connecting computer directly to one of
  > modem's LAN ports, obtained IP 192.168.1.4 and accessed modem's web UI
  > at IP 192.168.1.1
  
     If your "modem" were acting as a modem in bridge mode, then your
  computer would be getting its IP address from your ISP, not some private
  address like "192.168.1.4" from the "modem" itself. An actual bridge
  provides a simple, straight-through connection, and does not provide a
  DHCP server or NAT.
  
     You seem to think that you understand what's happening here, but I
  claim that you're wrong.
  
  > [...] As shown in the answer cited [...]
  
     So far, I see no relationship between what you're doing and the
  material in that discussion.
  
     As explained elsewhere, a router needs no special help to pass data
  from its LAN side to its WAN side. That's its whole purpose in life.
  - piotr_dobrogost
    Aspirant
    Mar 24, 2021
    > If your "modem" were acting as a modem in bridge mode, then your
    computer would be getting its IP address from your ISP, not some private
    address like "192.168.1.4" from the "modem" itself. An actual bridge
    provides a simple, straight-through connection, and does not provide a
    DHCP server or NAT.
    
    Apparently this modem seems to be in some kind of mixed/hybrid mode then :)
    R8000 connected to one of modem's LAN ports is perfectly able to establish PPPoE connection to my ISP through modem. R8000's web UI, section "ADVANCED Home", subsection "Internet Port" reports
    IP Address: <public IP address obtained from ISP>
    Connection: PPPoE
    Computer connected at the same time to another modem's LAN port obtaines IP address from modem's DHCP server and is able to access modem's web UI.
    
    The question is how to configure R8000 so that computer connected to R8000 can access modem's web UI the same way computer connected directly to modem can?
    
    In the other thread (https://community.netgear.com/t5/Nighthawk-WiFi-Routers/Nighthawk-R8000-DHCP-on-WAN-port-not-working/m-p/2066232/) You wrote:
    
    > If the TD-W8960N-as-modem is actually accessible at some IP address
    from its LAN side, then I'd expect it to be reachable through the R8000
    without doing anything to the R8000. From any system which is on the
    LAN of the R8000, if you try to reach any IP address which is _not_ on
    its own LAN, then I'd expect the R8000 to pass that message out through
    its WAN/Internet port, where it will reach the TD-W8960N-as-modem. You
    don't need any special routing to make that happen.
    
    This is logical but that is not what I'm observing in my situation. One thing that comes to my mind is that above would work on the condition that R8000 actually obtains IP address from modem's DHCP server but it seems that's not the case.
    TD-W8960N is accessible at 192.168.1.1 address from its LAN side but it's not accessible at this address from any host connected to R8000.
    
    You also wrote:
    
    > And if the TD-W8960N-as-modem has its own LAN subnet (because it's
    really still a router), then _it_ might need some special routing to get
    a message back to the R8000, but the R8000 would still need no changes,
    because it would still want to send any foreign-looking traffic out
    through its WAN/Internet port (to the TD-W8960N).
    
    TD-W8960N is configured with the subnet 192.168.1.0/24 and itself has 192.168.1.1 address and R8000 is configured with the subnet 192.168.10.0/24 and itself has 192.168.10.1 address. TD-W8960N has an active DHCP server with the IP range 192.168.1.2–192.168.1.4
    
    It looks like the problem is that R8000's WAN port does not in fact have IP address in TD-W8960N's subnet 192.168.1.0/24 and that is exaclty what solution given at https://superuser.com/a/993785/664 fixes by assigning such an IP address to router's WAN port.
    The question is how to do this using R8000's original firmware and not DD-WRT which is used in that solution?

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How to access modem from router when modem is in the bridge mode?