said by graysonf:
Your IPv6 default gateway is also a local link address and not a gateway to the internet.
The gateway should be LL. This is learned via RA.
What's odd here is that if you're directly connected, you should be getting a /128 prefix and not a /64 via PD.
In my area Comcast hands out /128's out of their 2001:0558::/29 prefix.
They hand out PD out of 2601::/28.
Did you just get v6 today? I wonder if something got botched during the turnup.
Second thing I would recommend is posting ipconfig /all.
Edit: I see you just got this today. Should probably open a ticket in the Comcast direct forums referencing this thread.