Cisco Small Business Voice Gateways and ATAs (Linksys Business Series)

Inability to access certain websites is due to three main factors:

1. Security on the web browser is set too high
2. MTU not set on the router properly
3. Secured websites  

Lowering Security Settings on Internet Explorer

Step 1:
Double-click Internet Explorer and click Tools.

Step 2:
Select Internet Options, click Security then Custom Level. A window similar to Step 3 will appear.

Step 3:
Under the Reset to drop down menu, select Medium-Low and then click OK.

Note: If this did not work, enable the MTU on the ADSL gateway. For instructions, follow the steps below.

Enabling MTU on the VOIP Router

Step 1:
Determine the proper MTU size for the website.

Step 2:
Access the router's web-based setup page. For instructions, click here.

Step 3:
When the router's web-based setup page appears, look for MTU and set it to Manual. Then on the Size field, enter the MTU value which you obtained from Step 1.

Note: The recommended MTU sizes for DSL and Cable Connection are the following:

Cable Connection: 1500 
PPPoE DSL Connection: 1492

Step 4:

Click .

Note: If this did not work, open ports on the router. For instructions, follow the steps below.

Opening Ports for Secured Sites

Step 1:
Access the router's web-based setup page. For instructions, click here.

Step 2:
When the router's web-based setup page appears, click Applications & Gaming then click Port Triggering.

Step 3:
Under Application, type "https" and under Triggered Range and Forwarded Range fields, type "443" (the port being used by https).

Step 4:

Click .