Network setup with multiple subnets

Installing and Using OpenWrt Network and Wireless Configuration
1

Hi,
I've always wanted to make "neat" network and just recently tried openwrt so my understanding of networks can be lacking :wink:
I want to setup network, build with three openwrt routers (2x TP-Link C6U and one C7).
What i want to achieve:

  • Each of 3 slave router having separate subnet (192.168.1.0/24 ... 3.0/24)
  • Devices connected to routers being assigned to matching subnet based on router.
  • Devices from two different subnets can communicate.
  • Each router configurable from any point of network (besides WAN of master router)
    ** Using one of routers as "master" router with subnet 192.168.0.0/29 only to connect other routers together.
    *** Separating lan ports of one of routers to have "two routers in one" (acting both as master and slave).

Effectively having fiber gateway connected to WAN of master router, two slave routers connected to master. And half of master acting as another slave.
I know easiest way to make it work is to use /22 subnet on just one router and use other two as dumb switches with static IPs.
Is it possible? And how to do it?
I can make some diagrams if my explaining got too convoluted.

2

Yes.

I think the first question to ask (and answer) is why do it, i.e. what do you expect the network to look/operate like as an end result and why do you want it to work like that?

You'd be adding a fair amount of complexity to your set up and it's not really clear why/what you're wanting to get out of it. It may be there's a much simpler way to get the end result you're after.

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3

Well,
There is no reason besides "it is cool".
I'm aware that it is unnecesary complexity, but i want to learn how to do it.
I've spend a lot of time tinkering with it as exercise, but with moderate results, i don't consider this time wasted, it was fun.
So in the end i will appreciate either whole solution or just tips what to do, because right now i am clueless.

4

Here is the DSA tutorial to separate the ports, the various roles an OpenWrt can have, the static routes and the firewall documentation.
Good luck!

Unless you have up to 1021 devices to connect to the router, this is not necessary. Most of the households can fit in a /24 subnet.

1 Like
5

Can we define neat?

neat = tidy
neat = interesting, cool

Your proposed network topology is not tidy, but it can be interesting.

A tidy network (in the context of a home or small business) would typically have all networks defined on the main router, and the other devices would serve as managed switches and dumb APs. It is easier to administer and troubleshoot a network that follows this paradigm and can often be more efficient unless you have high bandwidth inter-VLAN routing needs.

Your stated goal certainly is more interesting, and it allows you to learn, understand, and troubleshoot various elements of complex network routing.

This is, of course, not an issue at the surface. However, if there are wifi devices roaming between these routers, it will actually be a terrible experience since the devices will have to negotiate a new DHCP lease on each change event and then re-establish the network activities with the new address. This will cause significant latency and drop outs when working with anything streaming (think of video, gaming, video conferencing, etc.).

Wired devices would be fine in this scenario since they wouldn't be attempting to 'roam' between routers.

This very much depends on the type of communication required. mdns/zero-conf/bonjour/auto-discovery protocols (think airprint/airplay, chromcast casting, Sonos, etc) do not route across subnets. It is possible to do with the addition of mdns reflector/repeater packages, but this doesn't always solve the problem if a product is not using the standard mdns methods. (this is true, btw, even if the routing is all handled on the main router -- these zero-conf network technologies are designed to work within a single subnet).

So before you go this route (bad pun :rofl:), you should consider what devices/services live on each subnet and how they communicate. Also consider if the wifi will all be setup with a common SSID + password to enable roaming... if so, roaming across subnets is not advised as I described earlier.

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6

Thanks everybody for tips.
With this new knowledge probably topology will change but i will give it a try in a week time nonetheless.
On closing remarks, roaming is not an issue because each router would have different SSID either way.
I can't say i am surprised by something not working with such topology but lack of

still it is a bummer.

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