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.
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