During the 1990s, DSL modems were quite dumb and needed a wireless router to perform firewall duties and NAT (Network Address Translation) to allow multiple computers to safely use the internet. Today, DSL providers such as Verizon and AT&T are providing DSL modems that can do these things and more. Unfortunately, if the wireless router does the same thing, it often causes network lag from all the unnecessary firewall packet inspection and NAT. This is a case where the customer's equipment does too much and causes a problem.
The lag may be more prevalent in some operating systems but all computers will be affected to some degree. It may only show up in certain instances such as freezing Youtube videos after a minute or two.
Vista wireless lag (and Windows 7) usually comes from OS wireless features, but DSL users should look at non-wireless causes as well.
To prove that the double firewall and NAT is the cause, connect the computer to the DSL modem's data port directly and browse the web. Try to do something that would cause lag such as viewing a Youtube video or displaying a big flickr.com photo album. If there is no lag while connected directly to the DSL modem, then the double firewall and NAT may be the culprit.
The next thing to do is to connect the computer to a wired LAN port on the wireless router to see if the lag returns. If it does, then the double firewall and NAT is the likely cause
Configuring the Wireless Router to Remove Internet Lag
Ironically, the wireless router device needs to have its router capabilities disabled. Instead of going through the WAN port, all traffic should go through a default gateway which is the IP of the DSL modem. The DSL modem should be plugged into one of the normal ports of the router rather than the WAN port. The problem is that some wireless routers have no way of directing traffic other than through the WAN port. If traffic is allowed to go through the WAN port, the device will perform the unnecessary NAT and firewall functions. However, there is a workaround for this.
Configuring the DSL Modem to Remove Internet Lag
Another strategy is to to disable the router capabilities of the DSL modem instead of the router. The DSL modem will still negotiate the DSL connection but it will not pick up a WAN IP from the internet provider. Instead, the wireless router will pick up the IP instead and route all internet traffic. On Verizon supplied Westell 6100G DSL modem, this feature is called bridging. Disable the routed bridge mode and enable bridge mode in its place.
In some cases, the ISP may not allow the wireless router to take an IP unless it clones the MAC address of the DSL modem. Many wireless routers have a feature that allows MAC address cloning.
Installing DD-WRT Firmware
If some of the above features are not available to fix the lag, there is one other way to avoid buying another wireless router. Some devices are compatible with an open source wireless router firmware called DD-WRT. This free network router firmware extends the capabilities of most consumer grade wireless routers.
Because the installation of DD-WRT requires intermediate to advanced computer skills and voids the warranty on a wireless router, it may be preferable for some computer users to buy a device that has DD-WRT preinstalled.
By disabling the NAT and firewall features on either the DSL or wireless router, the network traffic usually experiences less lag from not having to perform NAT and firewall duties twice before going to the computer.
source: suite101
