DH Primes

http://tools.ietf.org/html/rfc3526

Why does OpenSSL have a specific optimized function for generating DH primes if standard primes for DH use have already been supplied?

>>1
OpenSSL has had it from the start (1998) and before that it was in SSLeay from the start (1995). RFC 3526 was published in 2003.
Also you might want to generate bigger groups or be concerned the NSA backdoored RFC 3526 or whatever.

>>2
That's not how DH works.