Trolling should result in an IP based ban.
It's all in the title. I have reported negative players for the entire time I have been playing league of legends. Yes, everyone has a bad game here and there, but that does not excuse the act of trolling the games of complete strangers who had nothing to do with a previous game. It is my consistent experience that trolls do so nonchalantly, and it leads me to believe that whatever consequences exist do nothing to deter the behavior. An account ban regardless of how long is placed on the single offending account, which are free. Trolls or other antagonistic players, who derive some pleasure out of antagonizing others and being counter productive, likely are smart enough to have a throw away account on which to be a troll. Changing an account is extremely simple, changing an IP takes more effort, and will help place emphasis on how seriously the problem is viewed.
Yes an IP may be shared with others, but consider that if the troll shares an ip with an honest and upstanding player, would that not also offer incentive for players in that close a proximity to behave more accordingly? Risking others is different than just oneself. This is not unlike the social pressures of real life, a troll likely does not act like this in real life, because there are tangible consequences there. "You are only as great as the company you keep."
I understand this punishment will be viewed as harsh by some, but what reasonable excuse can anyone really provide to justify leniency in the cases when players choose to become actively detrimental and toxic to the community. I even went on to read some published articles about why people troll, but the specifics of why aren't as important as the impact in this environment. One such impact is that not everyone has all day to play the games they enjoy, so when what little time they do have is willfully wasted by another, when the troll could have just as easily chosen not to play the game, it becomes extremely frustrating, very quickly.
In my opinion, trolling in a game means that the player is done with it. They are so jaded and bored with the expected play that it becomes risk of being punished vs psychological reward of trolling, and they will continue to do so until it becomes more work than it is worth to troll because it is currently very easy to do continue to do so.
Additionally, the reporting system feels empty and useless, zero feedback or transparency when you take the time to report makes it feel like reporting is pointless. Why protect the anonymity of a player who has become actively hostile and counter to the gaming culture you are trying to cultivate? I am guessing most people just hit play again and hope they don't meet another troll for a while, given how fast players leave the end game lobby after a game is trolled. That means players have given up on the system of reports in my eyes, they would rather move on as fast as possible and try to forget the negative experience because their efforts to fix the community are unrewarded/unrecognized.