just bought the cable modem t25 and it has the two ethernet jack in the back and i read somewhere that if i want to use the 2nd etherent connection than i need two different ip addresses from comcast. just seeing if thats true or i can just use the two with no problem at all?
Never heard of a "t25", but yes. It's true.
First, check the "Rate Card" for your local area to see if that feature is even available anymore. Seems that it is being phased out;
It's a PDF.
Scroll down to "Xfinity Internet" and look for "Additional IP Addresses".
If nothing is listed then it's likely to have been discontinued in your local market area.
Depending on the modem firmware installed, the second ethernet port can be used as a second IP node (as per above) or as a Link Aggregation Port (coupled with a compatible router or computer).
If you attempt to use both ports without configuring them properly you will get connection errors on one or both of them.