DH Selection For IPsec VPNs

Problem

What are the recommended settings for IPSEC VPNs?

Updated 25 April 2023

IKE:

• In general IKEv1 is still acceptable, unless you're dealing with a Cisco ASA which as of 2020 will only do SHA-1 in IKEv1

• ideal is DH-19 or DH-20
• minimum for reasonable security is DH-16, going below that is not recommended
• groups 1, 2, 5, 22, 23, and 24 are considered notably (and perhaps unexpectedly) weak.

• use AES-256 (or higher) with SHA-384 (or higher)
• Always avoid DES
• Avoid 3DES and/or MD5 if at all possible

References

• 2023-04, pfSense firewall v2.6.0-RELEASE (Community Edition) ipsec config pages
• 2021-08, NSA recommendations 2020: https://media.defense.gov/2020/Jul/02/2002355501/-1/-1/0/CONFIGURING_IPSEC_VIRTUAL_PRIVATE_NETWORKS_2020_07_01_FINAL_RELEASE.PDF
• some reddit thread somewhere which I can't find any more, yeah possibly sketchy AF maybe, but it's backed up by other places on the web
• 2019-03, NCSC (UK) requirements for their tunnels: https://www.ncsc.gov.uk/guidance/using-ipsec-protect-data
• 2018-10, DH group: https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solutionid=sk27054
• also some reddit thread somewhere which I can't find any more, yeah possibly sketchy AF maybe, but it's backed up by other places on the web