I'm mostly writing this post for me, but maybe it'll also help someone else. For the first series of the season mlb.tv was blacking out local games and Yankee games. Blackouts suck to begin with, but there was no reason that Yankee games should be getting blacked out for me out here in the DC metro area.
At first I assumed the problem was on mlb's side, maybe they were blacking out games for everyone to force you to watch them on ESPN? But when the second series started against the Diamondbacks I knew it was a technical problem so I opened a support ticket. Three days passed and they didn't get back to me so I started googling around until I found a reddit post that saved my bacon. If I can find it again I'll definitely link back to it, but that's part of the reason I'm doing my own write-up here, I can't trust reddit to keep that post forever.
Anyway, enough editorializing, here's the fix for my Veriozon Fios router:
The problem went away instantly, but I like IpV6 so I'm probably going to be turning it on and off all season (unless mlb fixes their stuff) and then forget again next season, so this is a reminder to myself about the hoops I jump through to watch baseball.