ISP Modem+Router -> Switch -> Switch -> OpenWrt Router

I've configured multiple WANs with OpenWrt before, but this is my first time doing so with a modem, and I need some help.

Here is what my network looks like:

The devices are:

  1. OpenWrt Router (TP-Link WDR3600) that connects to ISP1 via PPPoE. It is also connected to Smart Switch 1.
  2. Smart Switch 1 (TP-Link SG108E) - Connected to OpenWrt router, multiple devices, an access point (Unifi) and to Smart Switch 2.
  3. Access Point (Unifi AC-Lite). This is connected to Smart Switch 1.
  4. Smart Switch 2 (TP-Link SG108E) - Connected to Smart Switch 1, to a PC, and to ISP2's router.
  5. ISP2's (Reliance Jio Gigafiber, if it matters) modem(?)-router. Incoming link is fiber-optic. The router's WAN page shows DHCP as the connection mode. This is connected to Smart Switch 2. This router has 3 LAN ports.

ISP2's router has an option labelled "bridge", under which it gives me the option of choosing the ethernet port and a VLAN ID. However, one Redditor says that the bridge mode on ISP2's router does not work. ISP2's router has the address by default, and by default runs a DHCP and a DHCPv6 server. It seems to be getting a /128 PD via DHCPv6 from upstream. The router supports VLANs on the LAN configuration page, and allows me to assign a VLAN ID for each LAN port.

How would I go about configuring access to ISP2 on the OpenWrt device? Would the interface 'ISP2' on the OpenWrt be "DHCP Client" or "Static" or something else? How do I test bridge mode, and how would I know if it is working properly or not? Should I switch off the DHCP{v6} servers on ISP2's router?

Eventually, I'd want to use mwan3, but for now I just want to be able to connect to ISP2 from my OpenWrt router.

Alot of your questions are going to be influenced by;

  1. where internal dhcp services are
  2. whether or not your using the "smart" switches as smart switches....

Best to offer an overview of internal dhcp operation and or L2 isolation. As it stands.... just test using bridge in isolation. If it's reliable.... decide of you want to use it.... then decide if your tagging that across to router 1.... then test that..... the rest is nothing special.....

The whole setup is made or broken on layer two and internal addressing. Get your head around the addressing then mess with the isolation.... and go from there....


  1. I'd prefer to keep the OpenWrt router as the DHCP server.
  2. The smart switches support 802.1Q and port-based tagging, but I currently don't use that.

Frankly, I don't understand how VLAN tagging works well enough. Multiple devices (UniFi AP, my Linux PC, etc.) provide me the option of adding VLAN tags to a particular interface. If VLAN functionality is disabled on the switches, will the router still see the VLAN tag? Do the switches "strip" VLAN tags if it is no enabled? Will I have to enable 802.1Q / port-based VLAN tags on the switches for the VLAN tags to be visible to OpenWrt router?

I tried setting the ISP2 router in "bridge" mode with VLAN ID 5, but it was still being assigned a WAN IP address even after I did so and rebooted the ISP2 router. I created a new interface on my OpenWrt router named isp2, made it eth0.5 in the switch page in Luci, and set it to DHCP mode. But it didn't get assigned any IP. I'm not sure if I did something wrong, or if the "bridge mode" in the ISP2 router doesn't work.

How do I "test using the bridge in isolation"?

Like this

[ISP2GATEWAY] <--------------> [TESTCLIENT]

So, trying to put the modem in bridge mode didn't work. It seems likely that "Bridge Mode" on that modem is broken. Sources: 1, 2, 3. Any other ideas?