In order to get the blazing internet speeds that Shaw offers, I had to swap out my old Motorola modem and replace it with a new Cisco DPC3825 residential gateway.  The DPC3825 is essentially a DOCSIS modem combined with a wireless router.  For a new Shaw customer, this is a great combination because a separate router purchase isn’t required.  Previous Shaw internet service offerings only provided a cable modem, so a router was a must.

If you added your old router to the DPC3825, you could experience double trouble; not due to any shortcoming of the hardware, but to the way networking works.

Cisco DPC3825 Wifi Router

When you connect a router to a cable modem, the router gets a single external IP address.  The router provides internal IP addresses to any devices connected to it.  When you visit a web site with your browser, the request is sent over the router, through the modem to the server and back to your computer again.  What happens if you have multiple computers on the router?  Remember, the router only has the single external IP address.

This is the magic of network address translation, or NAT.  As data is sent out to the Internet, the router translates the internal IP address to the external address, and keeps track of how to route the incoming data back to the correct device/computer.

Back to the DPC3825… it has a router that is already doing NAT.  Adding an additional router means a double NAT, resulting in the source and destination information being modified twice.  When data is returned from the remote server, the routers generally get confused.  In this situation, you will probably only be able to browse the web, and not much else.

So what was the fix?  It was quite simple, after an hour of web surfing; the DPC3825 had to be placed into bridged mode.  The DPC3825 needed to have firmware downloaded, so the only way to get bridge mode was to contact Shaw and request the change.  Fifteen minutes later and I was up and running with my old router.

So, if you are experiencing the same issue, ask Shaw Customer Service Representatives to make the change for you.