Cameron Toner will serve half before he is released on licence. A £100 fine was imposed on the last charge where he went onto the pitch.
The incident happened in the first half of the match played at the City Ground as Nottingham Forest celebrated one of their four goals in the FA Cup win.
Addressing Toner, District Judge Leo Pyle refers to him jumping the barrier, running from the corner and touching the flag.
Judge Pyle told him: "It was a determined attack on Forest players and, in my view, was cowardly".
He is charged with assaulting Brennan Johnson, who was on the scoresheet during the memorable victory over Brendan Rodgers' side, as well as attacking forward Kenan Davis and star full-back Djed Spence.
Toner, of Station Street, Whetstone, has also been issued with a football banning order preventing him from attending any club or international matches for 10 years.
Douglas Mackay from the Crown Prosecution Service said: "We will not tolerate blatant football fan criminality and stand ready to work with the Police to prosecute such cases."There is no place for unauthorised pitch invasions in football and we want the game to be enjoyable for everyone and not have actions that could deter people from attending matches."