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Basic routing question

Discussion in 'Routers' started by routers, Apr 15, 2019.

  1. routers

    routers Occasional Visitor

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    First of all, I apologize if this is posted in the wrong forum. It's not clear to me where to post basic networking questions.

    I have a RT-AC56U with the latest Merlin firmware version for the model, but this is not a ASUS or Merlin specific question.

    I have two connections to the internet. A broadband and a 4G and I use Dual WAN to manage them and it works great.

    The question is about how I can get devices in different subnets to talk to eachother.

    Huawei 4G modem/router with build-in switch: 192.168.1.1
    PC1 connected to modem/router: 192.168.1.10

    Asus router getting WAN from the Huawei modem/router: 192.168.2.1 (double nat)
    PC2 connected to router: 192.168.2.20

    How can I get PC1 and PC2 to talk to each other?
     
    Last edited: Apr 15, 2019
  2. ColinTaylor

    ColinTaylor Part of the Furniture

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    You haven't said how/where the second internet feed (broadband) is connected in this setup.

    How is the Dual WAN set up, fail-over or load balancing?
     
  3. routers

    routers Occasional Visitor

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    Dual WAN. On the ASUS router, the WAN IP to both of these devices are 192.168.1.2. So the ASUS router is a client of both of these networks and it works great. When I turn off the 4G router, the WAN from the broadband connection takes over and give internet to all my devices. Said in another way, the Dual WAN is set up as failover so then I just can turn off the Huawei device and all my devices get internet from the broadband connection.
     
    Last edited: Apr 15, 2019
  4. ColinTaylor

    ColinTaylor Part of the Furniture

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    So your broadband feed comes from another router somewhere and that is connected directly to the Asus. Correct?

    And the dual WAN on the Asus is setup in fail-over mode with the 4G feed as the primary and the broadband feed as the secondary?
     
  5. routers

    routers Occasional Visitor

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    I use my ASUS router as a hub for all my devices (except PC1 in this example) where it is conneced directly to the 4G router/modems switch (where the ASUS router is also a client).

    My ASUS router: 192.168.2.1 where I have a lot of clients, like 192.168.2.xxx
    The ASUS router is getting internet from whatever Dual WAN connection is active.
    But the quesion is about local communication. Connecting 192.168.2.xxx to a device on 192.168.1.xxx
     
  6. routers

    routers Occasional Visitor

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    When I ping 192.168.1.client from 192.168.2.client
    Pinging 192.168.1.client with 32 bytes of data:
    Reply from 192.168.2.1: Destination host unreachable.
     
  7. ColinTaylor

    ColinTaylor Part of the Furniture

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    Can you ping 192.168.1.1 from a client on the 192.168.2.x network?
     
  8. routers

    routers Occasional Visitor

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    Yes,
    Ping statistics for 192.168.1.1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
    Approximate round trip times in milli-seconds:
    Minimum = 1ms, Maximum = 1ms, Average = 1ms
     
  9. ColinTaylor

    ColinTaylor Part of the Furniture

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    So you need to adjust the firewalls on the clients in the 192.168.1.x subnet to respond to ICMP from the 192.168.2.x subnet.

    Windows firewall for example will block ICMP if it doesn't originate from the local subnet.

    EDIT: Sorry, my mistake. If the router at 192.168.2.1 has NAT enabled then you shouldn't need to adjust the Windows Firewall rules as all traffic from 192.168.2.x will appear to be coming from the Asus' WAN IP address (192.168.1.2).
     
    Last edited: Apr 16, 2019 at 9:15 AM
  10. routers

    routers Occasional Visitor

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    PC2 is not rejecting connections. I want to connect via RDP and network shares but can't from 192.168.1.xxx.
    I know how to allow connections from and to PC2 (win10 1809) but - no success from 192.168.1.xxx.
    Ping is just the first "attempt" to connect before trying anything else.
    To troubleshoot further in case I missed something, how to allow ICMP from non-subnets on PC2?
     
    Last edited: Apr 15, 2019
  11. ColinTaylor

    ColinTaylor Part of the Furniture

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    PC2 is on the 192.168.2.x network so if you're connecting to it (from 192.168.1.x) then the traffic is going in the opposite direction. To make that work you need to;

    1) create a static route in the Huawei
    2) turn off the firewall on the Asus
    3) turn off NAT on the Asus
    4) adjust any firewall rules as necessary (this should not be needed for RDP)
     
  12. routers

    routers Occasional Visitor

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    Really? Ok due to time zones and sleep and work I'm unable to be here for the next 12 hours.

    I had the thought that I need to make a static route on the Huawei which I don't think is possible due to the limited settings.

    For now, thank you very much @ColinTaylor for your assistance.
     
  13. ColinTaylor

    ColinTaylor Part of the Furniture

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    Yes it was late here (4am) so I've had to correct my post #9.

    The static route and changes to the Asus' firewall are required if you want complete access to the 192.168.2.x network. Disabling NAT is optional, but if you don't do it then connections initiated from clients on 192.168.2.x will look like they're coming from 192.168.1.2 (which can be a bit confusing).

    The other alternative is to leave things as they are and setup port forwarding rules on the Asus for every service/device that you need to access on 192.168.2.x. You'd then access those services using the router's 192.168.1.2 address.
     
    Last edited: Apr 16, 2019 at 10:51 PM