If you are using encryption or authentication algorithms with a 128-bit key, use Diffie-Hellman groups 5, 14, 19, 20 or 24. If you are using encryption or authentication algorithms with a 256-bit key or higher, use Diffie-Hellman group 21.

Which Diffie-Hellman group is the strongest?

DH group 1 consists of a 768 bit key, group 2 consists of 1024 bit key, group 5 is 1536 bit key length and group 14 is 2048 bit key length. Group 14 is the strongest and most secure of the ones just mentioned, but there are other key lengths as well.

Is Diffie-Hellman Group 5 secure?

5—Diffie-Hellman Group 5: 1536-bit MODP group. Formerly considered good protection for 128-bit keys, this option is no longer considered good protection.