If I hadn't known better, I'd say def. mix. However, I brought my dog to the dog park, and this lady had 2 boxers.....one was 9 months old, and the other 2 years. The 2 year old had a long snout like your dog does, and didnt really look full boxer, although the colors and everything were that of a boxer. She saw both of the parents, and they were both full breed boxers. Your dog resembles this one quite a bit, although his nose wasn't quite as pointy, and he was brindle.