Being dog aggressive is not particular to dachshunds. It's usually a result of a dog that was not properly socialized in puppyhood, or did not continue with socialization to dogs outside his pack. Often, with small dogs, it is simply that the larger dogs overwhelm them, and in an effort to get the dog to play or be friendly, owners "overface" them, and instead of getting better, they get worse.
The OP might want to read "Scaredy Dog - Understanding and Rehabilitating Your Reactive Dog" by Ali Brown. Good stuff about how to desensitize the little guy so you can have pleasant walks.
You get what you reinforce, not what you want.
~ Bob Bailey
Disclaimer: The dog.com forum posting rules require that members post a disclaimer when linking to training or behavior sites. As a professional trainer, any advice or links I offer are based on my years of experience with my own dogs, rescued/shelter dogs, and my clients’ dogs, but still may not fit your individual situation with your dog(s). I advise that you seek competent professional advice before trying any training or behavior modification techniques on your own dog(s).