restriction may be numeric, a **getservent**(3) service name, or the special
value _opaque_ for RFC 4301 OPAQUE selectors. Port ranges may be specified
as well, none of the kernel backends currently support port ranges, though.
+ If the protocol is _icmp_ or _ipv6-icmp_, the port is interpreted as ICMP
+ message type if it is less than 256 or as type and code if it is greater or
+ equal to 256, with the type in the most significant 8 bits and the code in
+ the least significant 8 bits.
When IKEv1 is used only the first selector is interpreted, except if
the Cisco Unity extension plugin is used. This is due to a limitation of the