Around 4 months ago, someone learned my IP, and is threatening to DDoS attack me if I am not his slave. He was breaking the Discord TOS with all kinds of stuff in my DMs. I blocked him, but one of his friends told me to friend him back, or he will DDoS me.
What should I do?
ISP's have ways of dealing with DDoS attacks targeting one or more IP addresses on their network. See How can ISPs handle DDoS attacks? for some interesting reading on this subject.
What you are describing sounds more like online banter than a serious threat, and I would be surprised if your your adversary actually follows through with their threat (or even has the capability to do so). But, if he does attempt to mount a DDoS attack targeting the IP address that your ISP has assigned to you, and you are impacted by it - simply report it to your ISP and they can likely mitigate the problem using one of the methods in the above link.
He's trying to scare you into doing what he wants, but he has no means of harming you by knowing your IP. Feel free to block him and disregard anything he says.
Contact your ISP’s security team and explain your situation. They should be able to help you change your IP to a new address.
Not enough information for a qualified answer. I will make some assumptions and spell them out. Basic assumption: You actually care about being DDoS'ed (you earn money doing live streams or something).
First, I assume he means a static server IP address, not your home IP. Most ISPs use dynamic pools to assign IPs and you will get a different IP from time to time - sometimes every day, sometimes whenever you reconnect, depends on your ISP. If he means your home IP, you are good, because in 4 months you most likely have a completely different IP now.
Then again, a static server IP makes no sense to "find out". They're public. All it takes to "find them out" is "ping domain.ext" and there it is. Which also means that changing the IP doesn't do squat.
Second, I assume that he actually has the capability to make a DDoS attack of sufficient strength to knock your server offline. Most likely that will trigger the anti-DDoS protection of your hosting provider. It is still likely that your server will go offline. It is not likely that it will stay offline for long, as your hosting provider will take action - they don't like DDoS traffic clogging up their network.
Third, I assume that he doesn't have sufficient capability to knock your hosting provider offline. People who sit on that kind of botnets don't generally use them to threaten random people into "re-friending" them, that's just ridiculous. You can make real money if you have a proper botnet. He'd rather do that.
Conclusion:
Possibility a) we're talking about a server and a person who has the actual capability to run a DDoS. Advise: ignore him - sure he can knock you offline for a bit, but it'll cost him more than you and it won't last.
Possibility b) we're talking about your home IP. Then either - b1) the guy is a troll who's trying to scare you and he actually hasn't half a clue about how things work. You've most likely changed IP since then. ignore him, he won't harm you. Or b2) he keeps track of your changing IP and actually is only half an idiot. He could DDoS you and disconnect you, which might be shit during a game or a live stream. If so, talk to your ISP and report him to the police (threatening negative, illegal consequences if you don't comply with a demand is a crime). Also report his friend as an accomplice. Note that, depending on your jurisdiction, two people collaborating to commit a crime is sometimes enough to qualify the deed as organized crime - I'm not kidding. Once these people get involved, the shit hits the fan. Do not inform them that you've reported them. That could be construed as interfering with a police investigation.
Involving the police might seem harsh. I don't know the circumstances of your case. If you think "wait, no, that's not what I meant" then my basic assumption may be wrong and you will not be seriously affected by a potential DDoS. If the whole thing is mostly inconvenient and just scares you a bit, then ignore him and if he does eventually DDoS you, disconnect, read a book for an hour, come back and you probably got a new IP from your ISP and are online again. If not, call the ISP technical department and complain about a service outage. They'll figure it out, filter the DDoS traffic and put you online again.
The worst this person can do is interfere with your internet speed. They won't be able to "hack you" or do anything to your computer, nor will they be able to obtain any sensitive information from you just because they know your IP. Don't worry about any serious consequences. Of course, if you're a competitive gamer, losing a match because someone is attacking your IP can be frustrating.
You have three options: comply, refuse, or protect yourself. Complying and becoming this person's "slave", as you put it, is probably not what you want. Given that this is their demand, it's very possible that they're bluffing anyway. It's not like they're blackmailing you with life-destroying secrets. Refusing may result in your internet speeds being decreased or you even being temporarily disconnected from the internet, but that's all. Finally, protecting yourself is most easily accomplished by changing your IP. If you have a dynamic IP, then rebooting your router or simply waiting for a new IP to be assigned to you is sufficient. Otherwise, you'll want to contact your ISP and explain the situation to them. Simply tell them that someone is threatening to DDoS you. They may change your IP for you.
Although ISPs do have ways to protect from DDoS attacks, they can only do so much, and often their last resort is IP blackholing, which protects them (and their other customers) at the expense of the attacker's target (you). Unfortunately, many people can still perform DDoS attacks sufficient to knock someone off the internet for a short time despite mitigations than modern ISPs often use.
Discord is not P2P, so they didn't get your IP address from Discord, unless you clicked a link. This is where the HTTP proxy configured within your default browser will help. Generally, assuming you're a gamer, VPNs encapsulating your entire connection can negatively affect your ping/MS in game, which isn't great for gaming.
Furthermore, you can report this person to Discord here: https://support.discord.com/hc/en-us/requests/new
