Okay i need some help with a similar issue.
I got a Roku 2 XS for christmas. I tried to set it up to a wired connection (same ethernet cord I usually have my Xbox plugged in to). It could not connect to my local area network. My router is from Comcast with a model number of smcd3gnv. I called tech support and after an hour of resetting my modem also trying the wireless connection as well, they said they would mail me out a replacement in case it was defective. I felt like I was missing something so i tried it at a friends house, with "WOW! cable, and i got it to work via ethernet cable immediately. This led me to try to call my internet provider and ask them if they had any ideas. The woman I spoke to informed me that Roku is currently not supported via their modems, but if an update happened it would be posted on their homepage. I tried to confirm this fact with Roku when i called again, but they said there is no link between the two.
So, can someone tell me, is it possible that Comcast's modems are stopping me from using my Roku, and if so if there is a way to fix this/ will comcast fix this?
Let me know if i need to clarify anything, im sure i do.