probably discussed before, or basic(ally impossible), but I didn't find anything similar (probably as I don't have the right terms in my vocabulary).
In short: I want a device behind my OWrt router (LAN side) to be on the same IP network as the network infront of it (WAN side), because that "client" device shall see a "mother" on the WAN side and act as if it was physically directly connected on that WAN side.
Why? Well, distances, existing cabling, no wifi range.
Setup on more detail:
- The "Fritz" network (10.0.0.x/24) with the main router (FritzBox, aka "mother") on 10.0.0.1
Wired to WAN port on the OpenWRT box. - OpenWRT box "GL-AR300M16-EXT" (2x LAN, 1x WAN; only 1x LAN used atm.)
has 10.0.10.x/24 on its LAN1 side
Wired to a managed switch - Lancom GS-1224
Wired to - Ubiquity "ToughSwitch PoE PRO" (TS-8-PRO) (aka "EdgeSwitch XP")
From here I can run a LAN cable to - "Fritz Repeater" client device.
To allow the FritzRepeater to act as a member of the "Mesh" that those Fritz devices create both normally need to be on the same network. This "meshing" with the Fritzbox as the master enables the same wifi networks with e.g. parental controls, MAC filtering etc etc across all of them (meanwhile 4 across the premises...) so that clients can roam around easily. Yes, there's other systems, other hardware etc in the world, but that's what we have and would like to extend as described. So "why not buy proper stuff xyz" isn't in the solution basket here 
Now, is there a way to "tunnel" the 10.0.0.x network from the WAN side to that one client on the LAN side? Maybe by using the VLAN functionality of the lancom & ubiquity switch and the OpenWRT routers?
On the client repeater, I can set IP, Subnet, Gateway, and 2xDNS manually, so I could tell it to be 10.0.0.something/24 if DHCP wouldn't make it through the tunnel from the main router. But I can't tell it to look for 10.0.0.1 as the master - they somehow discover each other at the magic push of hardware buttons during pairing. So, maybe it would be sufficient if I had the "outbound" tunnel from the repeater towards the master, then it might be able to register the repeater when it "shouts out" onto the "tunneled" network and the master hears and responds and accepts the pairing. Not sure.
So, any ideas, can such be done?
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Scratching my head: Would I have to go through the OpenWRT at all? Or could I maybe simply build a "bypass" it:
- on the lancom switch, group all 10.0.10.x Ports as "VLAN1"
- for one free port, set VLAN2 tag
- connect the 10.0.0.x/24 "Master" LAN to the VLAN2 port
- for the port, that goes to the ubiquity EdgeSwitchXP, set VLAN1+2
- on the EdgeSwitchXP, set all ports which shall remain on 10.0.10.x to VLAN1, except for one which now becomes VLAN2
- connect the repeater to the VLAN2 port on EdgeSwitch
Would that enable a "double-use" of that one cable from Lancom to EdgeSwitch, and they do the "splitting/merging" of traffic? - Master FritzBox and especially Client FritzRepeater can't be configured with VLAN tags themselves- At least the Repeater for sure can't, so the switches would have to do the magic even if their connected clients don't tag their traffic.
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