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.
If you're teaming then multiple ports show as a single virtual port and only get 1 IP.
I have my setup with a MB8600 and 2 cables from there to my machine with LACP configured... Depending on how you have things setup you might have to add a delay statement of 3-5 seconds to prevent the system from not getting the same IP and requiring a reboot of the modem to get a new IP for the alternate MAC the modem is seeing as up first.
iface enp2s0f0 inet manual
iface enp2s0f1 inet manual
pre-up sleep 5 ##causes a 5 second delay at boot for the CM/MAC binding to be consistent
They are phasing it out but I'm going to escalate your issue to the Comcast corporate employees that are available to these boards. We've seen cases here where they have been able to get this accomplished for customers even when it is not listed in their rate cards, YMMV. You should get a reply here in your topic. Good luck !
So if it is not listed on the card for my area is there an unofficial way to get the 2nd ip??
@EG is right. However, I'd be more than happy to review your account to help determine if this has been phased out in your area or not. If you haven't already, can you please send a private message with your first and last name as it appears on your account? To send a Private Message, click on "Comcast_Support” and then click “send a message".