Unable To Connect To Internet When Connecting To LAN Is OK

Sometimes you may find that you can connect to your local network yet not have access to the internet.

Beyond the normal firewall and anti-virus tests, here are two other slightly more obscure items to check:

1) DNS – go to the CMD line and type in ipconfig/displaydns. This will show your local DNS cache. In some cases the DNS values are either corrupted or incorrect.

To clear the local DNS, type in ipconfig/flushdns

If flushing the DNS doesn’t solve the problem, you can disable and / or restart the DNS caching with these commands:

net stop dnscache
net start dnscache

2) ARP – This is the Address Resolution Protocol and it binds the IP with a physical MAC. You can see the values by typing in at the cmd line, arp -a

If you see any odd machine addresses, like 000-000-000, then you may have to patch the ARP table by using the arp -d and arp -s commands.

Unable To Get Consistent Internet Connection On Cox Cable With Motorola SB6141

I started to get intermittent internet using Cox Cable, a Motorola SB6121, and an ASUS RT-N66U router. After buying a new router and swapping the SB6121 for an SB6141 I still had the problem. The internet would work OK for a while — sometimes 10 minutes, sometimes for a few hours — before giving up completely. The only way to revive the connection was to reboot the modem and the router.

I finally give in and called Cox who sent a technician and found the power levels to be out of range. He replaced a small attenuator that is connected between the modem and the Cox coax and everything worked fine.

He told me the Power TX levels for my area should be from 35-52 and RX level should be between -10 and 10.

Looking at the SB6141 I can now see what the levels should be under the Signal tab. That info can be accessed on the SB6141 by going to 192.168.100.1.

Click on the image below to see a larger version.