Need to build a plain router, no NAT; no AP

Installing and Using OpenWrt
1

I've added USB ethernet dongles to a PI 4, intending to setup routers on my research net.

I don't want NAT, just want to route among 4 networks with
main net: 192.168.1.0/24
net 1 192.168.1.8 ----(pi one) --- 10.0.1.0/24
net 2 192.168.1.9 ----(pi one) ----- 10.0.2.0/24
net 3 192.168.1.10 ----(pi one) --- 10.0.3.0/24

I have no need for an AP environment in this (covered elsewhere)

Is it possible to bring an openwrt instance up as a multiport router in this config?

thanx

2

You can easily have 3 networks behind the OpenWrt router, but all of the upstream ones (on 192.168.1.0/24) are the same network. Why do you have 3 addresses in your scheme (.8 - .10)? You only need one address on that network.

4

2 answers:
1-- i'd started with 3 pi's and then consolidated but didn't edit the post. apologies.

2-- so far i've found the networks only function as NAT'd, perhaps I'm missing something in the config.

I want to be able to route between nodes on each of the 3 10.x.x.x networks as well as up to nodes on the 192.168.1.x net, but no luck.

in example 10.0.1.5 cannot directly access 10.0.2.3 by its IP, nor can 10.0.1.3 or 10.0.2.3 be directly accessed by nodes on the 192.168.1.x network.

Glad to discover there is someway to 'route' between the networks.

thanx

5

All it takes is to uncheck masquerade checkbox in all 3 zone forwatd rules.

1 Like
6

I'm setting a similiar thing on openwrt on x86 with a dozen of subnets in vlans.

I don't see any problem why this should not work - just omit (leave unconnected, disable, unconfigure...) anything you don't need/want.

In my case, I haven't deleted the WAN yet - just disabled, since I plan to use it for upstream as soon as my new setupt gets online. All my testing vlans are routed by the openWRT box like a charm - providing the firewall configuration allows this, resembling quite the setup you're describing.

If your 192.168.0/24 is supposed to be upstream link for the other subnets, the clients sitting there need to be told so by appropriate routes.
The easiest way to do so is to give your router an IP-addres in each of the subnets and tell the clients by DHCP to use your router (at the particular subnet) as default router. This is default behaviour of dnsmasq, anyway.
Of course, you also can do this by static config on any or some of the clients.

btw: on my old router, I perform redundant NAT although I connect to an upstream router from the provider, which does NAT, too. No need (any more), but does not hurt. May give you some extra comfort if you don't want to trust your provider.
When I installed that first, nearly two decades ago, my uplink was changing every couple of years, sometimes providers wanted to limit the number of clients allowed, this all I could hide by this solution. Later then I simply "forgot" to remove it.

7

Three things are required:

  1. Your upstream router must support static routes. If it doesn't, symmetric (non-NAT) routing will not work.
  2. You need to disable NAT Masquerading on the wan/upstream interface.
  3. You need to enable forwarding from wan/upstream > lan/downstream.

EDIT: Per @mk24 's comment below, adding the static routes for the upstream router, making the assumption that the OpenWrt router in question will hold 192.168.1.8 on the upstream network):

  • 10.0.1.0/24 via 192.168.1.8
  • 10.0.2.0/24 via 192.168.1.8
  • 10.0.3.0/24 via 192.168.1.8
  • (alternately, a single static route could be used: 10.0.0.0/22 via 192.168.1.8; this covers 10.0.0.0-10.0.3.255)
2 Likes
8

And you have to install a return route to each LAN in the upstream router. The next hop to one of the Pi LANs would be the IP of the corresponding Pi on the upstream network.

1 Like
9

will check out some of the points...

The routing is no issue, i do static routing for other generic *ix boxes, where i cant OSPF things.

10

Then use bird2 on openwrt to participate in an ospf area?

11

for something as simple as PI routers in fixed test nets... static is easiest