What happens when I plug a router into another router?

Question

I've recently switched ISPs, and the new one provided me with a modem (that what you call those things?) that doubles as a router.

I used a router on my previous ISP for wireless networking, but I've since taken it out of the equation to simplify things.

Basically, my setup went from:

WiMax Cable -> Modem -> MyRouter -> PC/Laptop

To:

Broadband Cable -> Modem/Router -> PC/Laptop

But, there are some problems.

For one thing, my ISP forbids me from changing my router password. I'm not concerned about security, as the password is long and complex enough, but that's the problem - every time a guest comes over and asks for access I have to recite this long string from a box. I'd much rather have my own password that I change regularly.

Second, during times of questionable connectivity, I often restart the modem. And I'm pretty sure that would also take down the wireless network, right?

Finally, the modem/router's range is pretty poor. My own router can at least spread the connection beyond the house. This one can barely push it out of the room it's in.

So, I want to change my setup from above, into this:

Broadband Cable -> Modem/Router -> MyRouter -> PC/Laptop

I'll be treating the Modem/Router as a Modem and plug in to my router via LAN cable.

What I want to know is:

• Will it affect my internet connectivity / introduce latency etc., etc.
• Will it affect my network / jumble up IP addresses and make local connections more of a pain than it already is.

Thanks.

Solution

If you are unable to make changes to the ISP router, then I would use your own wifi router, but use it as a layer 2 device, rather than as a router.

All this means is that the devices that connect to your router are on the same network as if they were connected directly to the ISP router.

The way to do this is to disable DHCP on your router, and connect it to the ISP router using LAN ports. This is important. Your router probably has a WAN port - ignore this and connect one of the lan ports to the router LAN port.

Now anything that connects to your router will issue a DHCP request for an IP address. Your router DHCP will be disabled, and as the LAN ports are connected, the ISP router will see the DHCP request and respond.

This is far simpler than the alternative of trying route twice. I would recommend disabling the wifi on the ISP router if you can, otherwise it is just using up radio bandwidth.

Comments

[Paul]

Your router password and the wifi shared key are different things. Most likely the ISP needs your router password to stay the same for managemnt purposes. However, changing the wifi key is something you should absolutely do.

[Jon]

@Paul Why would your ISP need the router password to be the same? And how would they know if you change it? Can they change settings on my router remotely?

[zack_falcon]

@Paul You're right about the WiFi shared key - that's exactly what I saw, and not router password. My mistake. It offers no option to setup a router password, though. We connect with the WiFi shared key - which management said I cannot change because maintenance blah blah blah.

[Ben Plont]

If they're "smart" routers they'll configure themselves and adjust the routing tables. You might need to make (or buy) a crossover patch cable (TIA-568A on one side TIA 568B on the other side). The wireless LAN shouldn't lose connectivity inside itself when the modem is rebooting, but you will loose internet connectivity.

[zack_falcon]

@BenPlont Actually, I just planned to use the modem/router as a modem and plug it into my router via LAN cable. I'm not sure if any of them are "smart" - probably not, though.

[Paul]

@Chipperyman I have no idea why the OP ISP would place such restrictions on their service. It is poor practice.

[zack_falcon]

Well, actually, what I did as soon as I got home was just plug the modem into my router via a LAN cable - there was no WAN port. It was internet to internet port. I've yet to disable DHCP, but upon checking my sister's laptop's IP and mine, it was 192.168.1.120 and 121, respectively. I'm not entirely sure what disable DHCP does - a way to connect those who connected via the modem/router and those to my router via a single network? If so, wouldn't that mean turning off the modem/router shut down the network as well?

[Paul]

@zack_falcon If you don't disable DHCP on the router, there is a chance it will respond to DHCP requests itself, and potentially give people an IP address in a range that is different to one that is routed out to the internet, or an address someone else is using, or the wrong gateway.