used. B<res> points at a pointer to hold the start of a B<BIO_ADDRINFO>
chain.
-For the family B<AF_UNIX>, BIO_lookup() will ignore the B<service>
+For the family B<AF_UNIX>, BIO_lookup_ex() will ignore the B<service>
parameter and expects the B<node> parameter to hold the path to the
socket file.
All other functions described here return 0 or B<NULL> when the
information they should return isn't available.
+=head1 NOTES
+
+The BIO_lookup_ex() implementation uses the platform provided getaddrinfo()
+function. On Linux it is known that specifying 0 for the protocol will not
+return any SCTP based addresses when calling getaddrinfo(). Therefore if an SCTP
+address is required then the B<protocol> parameter to BIO_lookup_ex() should be
+explicitly set to IPPROTO_SCTP. The same may be true on other platforms.
+
=head1 HISTORY
The BIO_lookup_ex() function was added in OpenSSL 1.1.1.