I know this is very basic question, but I don't have prior experience of setting network environments with multiple routers and no matter what I try I can't get the configuration working.

So, I have two routers, A and B. A is a dumb fellow (no DDNS, VPN, etc. fancy features) provided by my ISP and its duty is to bridge PPPoE to router B (ASUS RT-AC68U) and provide telephone access (not possible with B). A must be connected directly to WAN. PPPoE bridge works fine, meaning that I can access internet from Subnet B and DDNS in router B works. However, I can't access either Internet nor subnet B from subnet A. ping from laptop throws Transmit error: code 1231, and ping from PC throws Destination net unreachable.

Router B has DHCP server running, whereas A does not, in order to make sure two DHCP servers don't mess up each other.

I tried adding static route to B ( gateway:, but it didn't seem to work. I also tried adding static route to A ( gateway:, but it didn't work either.

What kind of routing, gateway, etc. settings do I have to set in each router in order to get access between the subnets? Access to Internet from subnet A is not necessary. Instructions preferably in noob format, as I'm not expert when it comes to routers and routing.

Routing table of B:

Destination     Gateway         Genmask         Flags    Metric Ref    Use Type Iface
<external 1.>   *      UH       0      0        0 WAN0 ppp0        *      UH       0      0        0      tun21        *        U        0      0        0 LAN  br0   UG       0      0        0      tun21
<external 2.>   *          U        0      0        0 MAN0 eth0
default         <external 1.>         UG       0      0        0 WAN0 ppp0

The topology:


  • I already explained you that writing "router" makes no sense, because a router to be a router must be connected at least to two IP networks and it must have at least two different addresses from these separate networks. – techraf Dec 17 '16 at 11:09
  • I don't quite understand what you mean. Router B is connected to internet via PPPoE connection, has thus public IP and private IP as shown. – Kitanotori Dec 17 '16 at 11:30
  • No, each of your routers on your diagram has one address. While Router A should have four and Router B should have three. – techraf Dec 17 '16 at 11:31
  • Sorry, but I don't understand what you mean. – Kitanotori Dec 17 '16 at 11:33
  • @grawity Of course it's a nonsense from the configuration point of view. But for the diagram to be valid and understandable, it must list four addresses. – techraf Dec 17 '16 at 11:38

I like this question, old though it might be.

Some conceptual items:

  • Routers should typically be drawn between networks because they provide a "route" (or path) from one to the other.
  • They can be connected to as many networks as they are capable of, and they will have an IP address on each.
  • You don't need more than one physical link between routers, to answer the implicit question related to the two links between router A and router B.
  • Any physical link between two routers should be represented as a network on the layer-3 diagram (it can be a network that other hosts or routers are connected to).

In your diagram, I would place router A between the Internet and subnet A.

I would place router B between subnet A and subnet B, meaning that subnet A is also used as a routing network between subnet B and the Internet.

In order for the routing network to work out correctly, router B must be configured with router A as its default route to the Internet. Also, router A must be configured to recognize router B as the correct direction for traffic to subnet B.

That probably looks like:

  • Router B:

    • IP1: netmask:
    • IP2: netmask:
    • Route: Net: [default], gateway:
    • Note that the networks and are defined implicitly and are local to this router. Only the Internet needs an explicit route.
  • Router A:

    • IP1: [Internet IP via PPPoE]
    • IP2: netmask
    • Route: Net: [default], gateway: PPPoE
    • Route: Net:, gateway:

IP setup is wrong rout A router B router B connection wan to LAN remove LAN to LAN both routers should have same subnet and DHCP running

  • 1
    if its to extend your network then one router should use DHCP server up and running the other should get the IP from it in that case remove wan to LAN and make LAN to LAN but than its not a subnet. you find more info if you search how to setup routers in cascade – hendrik Jul 30 at 3:17

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