The level must be set to one of the following: default, use, require, or unique.

• default means that the kernel should consult the system default policy defined by sysctl(8), such as net.inet.ipsec.esp_trans_deflev. See ipsec(4) regarding the system default.
• use means that a relevant SA can be used when available, since the kernel may perform IPsec operation against packets when possible. In this case, packets can be transmitted in clear (when SA is not available), or encrypted (when SA is available).
• require means that a relevant SA is required, since the kernel must perform IPsec operation against packets.
• unique is the same as require, but adds the restriction that the SA for outbound traffic is used only for this policy.

You may need the identifier in order to relate the policy and the SA when you define the SA by manual keying. You can put the decimal number as the identifier after unique like unique: number. number must be between 1 and 32767 .

If the request string is kept unambiguous, level and slash prior to level can be omitted. However, it is encouraged to specify them explicitly to avoid unintended behavior. If level is omitted, it will be interpreted as default.