Poor Performing Internet Speeds on Upgraded DSL Service

Had a customer recently upgrade their DSL service from a lowly 1.5Mbps to a whopping 11Mbps.

Now before you harass the speed of the service, when your out in the boonies and the closest thing to civilization is the road a mile away, you take what you can get.

Service technician from the DSL provider change out their older modem with a newer one. That tested fine on his laptop, but he couldn’t access the configuration screens when he hooked the customers network cables back in.

The previous modem also doubled as a switch for the network. Customer only has 4 Ethernet devices total so all lines are plugged into the switch portion of the modem. So he replace the new modem with another new modem in case the first new modem was bad. Programmed in the PPPOE values and standalone it worked fine. When he hooked that to their network, again he couldn’t get to the configuration screens.

First thing I notice is that the DSL LAN IP is not the same as the previous one. Server onsite is DHCP’ing different addresses as well. So I dig into the configuration screens of the Zxyel DSL and couldn’t find a place to change the LAN IP of the modem. I disable the DHCP services of the modem as well. What to do… leave the DSL on it’s IP and change the network.

Since they have a SBS 2003 server the best thing to do is to run the Change IP Wizard. The wizard runs fine and everything including the DHCP and DNS screens are changed as expected. Had to clean up some old stray IP’s in the DNS, but a restart of that service worked wonders. Coded the new DNS numbers from the DSL service provider into the DHCP scope, refresh the workstation IP to let the new numbers propagate and test the Internet speeds at Speedtest.net and Toast.net. Damn, still slow… if at all.

I noticed that sometime the pages would load, and sometimes they wouldn’t. DNS. Plugged in manually to the workstations the DNS of Comcast (, OpenDNS ( and Google ( Wonder of wonders it was fast as expected for 11Mbps. This got me wondering why the DSL provider would issue such lame DNS numbers automatically and how to figure out before hand if the provided numbers would be good resolvers or not.

So my search led me to www.grc.com and their excellent DNS testing tool: DNS Benchmark

After downloading and running the extremely small application I could see the DNS resolvers response times. One was in the bottom of the speed tests and the primary number (DNS1) didn’t respond at all. It was effectively a dead server.

Back to the DHCP scope. Removed the offending provided Name Servers IP’s and inserted OpenDNS and Google’s Name Servers while retaining the local DNS server first in the list. Refreshed the IP stack on the workstations and tested again. Speeds went from non-existent to snappy all with pages we accessed.

So moral of the story is don’t always trust that your provider has the best DNS numbers for your location. Do your own tests and tools like GRC’s can make your Internet experience bearable again.

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