IPsec protection policies can use any of the security mechanisms. IPsec policies can be applied at the following levels:
On a system-wide level
On a per-socket level
IPsec applies the system-wide policy to outbound datagrams and inbound datagrams. Outbound datagrams are either sent with protection or without protection. If protection is applied, the algorithms are either specific or non-specific. You can apply some additional rules to outbound datagrams, because of the additional data that is known by the system. Inbound datagrams can be either accepted or dropped. The decision to drop or accept an inbound datagram is based on several criteria, which sometimes overlap or conflict. Conflicts are resolved by determining which rule is parsed first. The traffic is automatically accepted, except when a policy entry states that traffic should bypass all other policies.
The policy that normally protects a datagram can be bypassed. You can either specify an exception in the system-wide policy, or you can request a bypass in the per-socket policy. For traffic within a system, policies are enforced, but actual security mechanisms are not applied. Instead, the outbound policy on an intra-system packet translates into an inbound packet that has had those mechanisms applied.
You use the ipsecinit.conf file and the ipsecconf command to configure IPsec policies. For details and examples, see the ipsecconf(1M) man page.