Why do I need Bridge mode on my main router to connect a second one?

Question

I want to buy a better router than the one my ISP provides me. I can’t just ditch my ISP router because it is modem and router at the same time.

What I’ve been told is that I would need to set my ISP router in bridge mode to have a second one managing all my home network.

My ISP router doesn’t have a bridge mode option. I’ve been told that I could use a DMZ configuration and it would be the same.

My true question is why do I need my first router with bridge mode in the first place?

Example: I connected a old router I have to the ISP router. LAN port on my ISP router, WAN port on the “old” one. Addresses of 192.168.1.x in my ISP router, 192.168.0.x on the “old” one. Everything seemed to work fine on both routers. I was told that with this configuration I would have no internet access in the “old” one, but I had.

Answer 1

Bridge mode from a modem/router is a cleaner, less risky setup than router-to-router.

“My true question is why do I need my first router with bridge mode in the first place?”

You answer your own question at the beginning when you say:

“I can’t just ditch my ISP router because it is modem and router at the same time.”

So you don’t want the router functionality. But to bridge between whatever connection your ISP has to your new router, it is best practice to just (effectively) disable the router aspect of your ISP provided modem/router so the device is just a modem.

As a modem, it bridges whatever their connection/protocol from the ISP to you is — coaxial cable with DOCSIS or RJ45 with ADSL and such… — to Ethernet protocol your router can handle.

Again, this is the best practice since there is one step from ISP to Ethernet and then from Ethernet to your new router. But if there is no obvious Bridge mode on that modem/router your options are limited as you explain.

“I’ve been told that I could use a DMZ configuration and it would be the same.”

Well, it would technically “work” but you introduce a layer of complexity that is really unnecessary at best, problematic at worst.

Connecting that modem/router to another router means you are hopping between two networks int your home to get outside. If done right, it can work fine without any issues. But if not, you could end up with — for example — two DHCP servers fighting it out and confusing the network. Which could lead to slowed down connections at best, crazy and unpredictable “outages” as the two routers fight to control the network at worst.

If you can’t really get a true Bridge mode on that modem/router then I would recommend the following steps to neuter network management on the modem/router:

• Disable DHCP on the Modem/Router: Your new/preferred router should handle that.
• Assign a Static IP Address to the New Router: With DHCP dibbled, assign a static IP address to from the modem/router to the new/preferred router.

That should work.

But again, it’s just there is always a risk that your ISP provided modem/router might get in the way of things. So it’s always better to just go to Bridge mode.

Inquire with the ISP if there is anyway for you to exchange the modem/router for a plain modem. I doubt that option exists with your ISP based on what you have described, but still it is worth asking about.

Answer 2

Bridge mode just turns your existing router into a 'just communicate with the ISP, and do nothing else' mode. No firewall/DHCP/NAT etc.

This mode means you can then attach your router to the ISP's router via your WAN port. Depending on what router you have, you may have some extra features. Check the ISP's or other forums as I have had a TALK-TALK supplied router that had some hidden options to do this for you, but it wasn't easy and did take a little knowledge.

You can do this without bridge mode but you will have problems with port forwarding, especially if you use a security camera NVR/DVR as it will have trouble communicating externally.

If you are using a cable modem for your internet - the type that does not use a phone line, and the ISP has suggested bridge, ask if they can send you a bridge-mode enabled router or enable bridge mode for you.

If your internet connection uses a phone line then you have a huge choice of alternative routers, as long as they let you have the connection login details so you can configure it.

Answer 3

You not need ISP Bridged Mode to connect your own router. Connect your own router to do all you need. Then there is no need to use the ISP router portion of the modem although you can if you wish . That is not affected by bridge mode or no bridged mode.

Follow up note: DMZ is not bridged mode and does not do the same thing. Since you do not have bridged mode available to you, then non-bridged mode works fine (which is why you got Internet in your post above). You are still secure this way, depending on how you set up / secure your router.

If you need access to your network from outside, you would need bridged mode to accomplish this and then would have to discuss with your ISP how this would be achieved.