The F5 BIG-IP appliance IPsec VPN must use AES256 or greater encryption for the IPsec proposal.

Without confidentiality protection mechanisms, unauthorized individuals may gain access to sensitive information via a remote access session. Remote access is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, nonorganization-controlled network. A block cipher mode is an algorithm that features the use of a symmetric key block cipher algorithm to provide an information service, such as confidentiality or authentication. AES is the FIPS-validated cipher block cryptographic algorithm approved for use in DOD. For an algorithm implementation to be listed on a FIPS 140-2/140-3 cryptographic module validation certificate as an approved security function, the algorithm implementation must meet all the requirements of FIPS 140-2/140-3 and must successfully complete the cryptographic algorithm validation process. Currently, NIST has approved the following confidentiality modes to be used with approved block ciphers in a series of special publications: ECB, CBC, OFB, CFB, CTR, XTS-AES, FF1, FF3, CCM, GCM, KW, KWP, and TKW.

From the BIG-IP GUI: 1. Network. 2. IPsec. 3. IPsec Policies. 4. Click on the Name of the IPsec Policy. 5. Verify an AES256 or greater encryption algorithm is selected. If the BIG-IP appliance is not configured to use AES256 or greater encryption for the IPsec proposal, this is a finding.

From the BIG-IP GUI: 1. Network. 2. IPsec. 3. IPsec Policies. 4. Click on the name of the IPsec Policy. 5. Configure AES256 or greater encryption algorithm. 6. Click "Update".