While it looks as if Brock, 25, will be a long-term starter, it is unclear what the rest of the unit will look like next season.
The current starters are Carlos Rogers and Tarell Brown. Rogers will be 33 next year and is set to make $6 million. The 49ers could consider releasing him or asking him to take a pay cut. Brown is set to be a free agent, although there was a report last month that the team was close to re-signing him. General manager Trent Baalke said San Francisco would like to keep him, but with Brock signed there are no guarantees.
But there is the possibility Brock and Brown will be the starters next year.
A wild card is veteran Eric Wright. He was signed this year and made his 49ers debut last week. The team likes him and he could be in the mix, but he signed a one-year deal. The team will also have Chris Culliver, who's out this season with a torn ACL. He is a solid player, although his contract is up after next season.
The 49ers could also use an early draft pick on a cornerback. The future of this position is still up in the air, but there is now some clarity with the Brock deal.