Too many unknowns here.Are they really fighting or just roughhousing as dogs do? If your walking your miniature poodle on a public sidewalk w/ a leash and he gets charged by a Rottweiler,you need to report the owner of that dog. If you live in the country where dogs seem to rome loose on their property and the dog runs out to the road when you go by and your afraid for your dog,speak kindly with the other owner about it.Or just let them go,dogs seldom fight to the death,once they know who the boss is they'll be friends.
If the dog is running around the street unrestrained, talk to the owner. If they do nothing, talk to animal control. If the dog is behind a fence, restrained or just unable to physically get to you and your dog, then keep walking and ignore the other dog. OR You could try walking in another direction.