Are shields subject to armor/magic resist damage reductions?

Shields act as health - which means that they have the same damage resistances as the character they were used on. This means that, for instance, a 1000 hitpoint shield will only give 1000 points of absorbed damage on a champion with 0 armor and MR. Usually, it's a fair bit more than this.

The thing is, in League of Legends, it's much easier to increase offense than defense. Carries are focus targets to begin with, so even a 1000 point shield goes down fast under 3-4 different champions attacking it. Most endgame carries can crit each other for over 600, easily.

Ultimately, shields might go down fast, but you are effectively giving them temporary health, not a simple damage reduction.