RHEL 9 IP tunnels must use FIPS 140-3 approved cryptographic algorithms. GROUP ID: V-258232 RULE ID: SV-258232r1045440 Overriding the system crypto policy makes the behavior of the Libreswan service violate expectations, and makes system configuration more fragmented.
Solution
Configure Libreswan to use the system cryptographic policy. Add the following line to "/etc/ipsec.conf": include /etc/crypto-policies/back-ends/libreswan.config