What are the disadvantages (if any) of accessing the internet through two or more "chained" routers?

My Problem

I just got internet setup in my dorm room at school through a third-party provider. The modem they gave me, however, also functions as a wireless router. I also have my own router with DD-WRT on it, which I would much prefer to use over their... not so good built-in router.

Terminology

• router-modem: The router-modem combination given to me by my internet provider
• router: My personal router

My Solution

Simple. I just connected the WAN port on my router to the first port on the switch of their router-modem combo thing. Then, I disabled the WiFi on the router-modem, and disabled the firewall completely (effectively making the entire thing a DMZ, as DD-WRT has a built-in SPI firewall).

Just to note this, the IP address on my router is set statically, and DHCP has been disabled on their router-modem. There are no other physical connections to the router-modem other than my router.

My Questions

• Are there any disadvantages to what I'm doing?
• Am I somehow circumventing any of the protection features of the SPI firewall by doing this?
• Will it result in any excess lag when trying to play online games? (due to the additional hop each packet needs to traverse)

The amount of lag is too small to notice. I have 3 routers chained together in my house and don't have any problems. Your DD-WRT firewall will still function and protect you.

The only thing you didn't mention explicitly was whether or not you disabled the DHCP on the modem/router. I would think you want your DD-WRT to handle the managment of IP addresses. Either way, you'll need to turn off one of the two so you don't get conflicts.

Sounds reasonable to me. The firewall should work by blocking packets somehow, and having another hop outside the firewall should do nothing. I wouldn't think that adding another very short hop via Ethernet would affect ping time or bandwidth.

The potential downsides as I see them are that you are removing their firewall and their wireless, and substituting your own. It is conceivable that their firewall is better and/or their wireless more secure. Unless you're substituting WEP for their WPA or something, I doubt there will be a problem.

There is nothing wrong with this setup. As a matter of fact using two routers in this way is a good way to protect your LAN from a potentially more dangerous network. Your bandwidth will not be affected in any noticeable way.

What you are essentially doing is adding another hop to each packet. The delay induced by this extra hop (assuming ideal networking hardware - which any modern post-2000 thing will do extremely quickly) will be much less than 1ms.

I'd say you're good to go!