Dog May Have Trouble Getting Along?

Yesterday, i introduced my oldest dog to my new puppy that i got. My oldest dog is a black lab/australian shepherd mix and my new puppy is a border collie. When i introduced them they seemed to be getting along just fine. So the next day i put them in the garage together, and of course i put my puppy in the pet porter, and they got along fine in there as well. I brought them in the house later today, and we were watching them in the living room, and my senior dog snapped at him. From what i saw, the puppy did absolutely nothing and the dog just randomly snapped at him, and i am afraid that they will never get along. Can someone please help me find a way for them to get along?