This INTEGER (group1, group2, ... group5) is described as identifying the Diffie-Hellman group used for this IKE Crypto Map when a PFS feature is enabled in the map's flags. An admin picks a stronger group for better cryptographic strength at the cost of more CPU-intensive key exchange computations during each rekey. For example, an admin hardening a tunnel to a financial partner might select group5 here instead of the weaker group1 once PFS is turned on in the crypto map flags.