Has he been at a dog park, kennel, pet store, vets office as of late?
Any other symptoms?
Dogs do not get colds such as humans do but they can get different forms which are similar. He can have Kennel Cough which is very common in dogs. I understand he is up to date on his Bordetella, but even with the vaccination a dog can still sometimes get Kennel cough or Parainfluenza. While this is most commonly transferred in kennels it can also be picked up just about anywhere from dog parks to vets offices. Parainfluenza is the most common and most contagious of the dog colds, and is passed by the sneezing of the dogs.
You can bring him into the bathroom and run hot water to create steam to help break up any congestion he is having. A warm wash cloth can be used to gently clean the eyes. Make sure he is eating and drinking. You can give him some unflavored pedialyte to prevent dehydration from the dog cold. Rest and time is the best cure unless it gets worse. You can take him to the vets office to make sure it does not become a infection. Your vet can prescribe nose drops and cough drops as well to help clear this up. Your vet may also want to prescribe a antibiotic to help get him over this faster.