How to create an ACL

-- step 1: Create the Access Control List and its Privilege Definitions
BEGIN
DBMS_NETWORK_ACL_ADMIN.CREATE_ACL (
  acl          => 'my_acl.xml',
  description  => 'Limit the use of package utl_http til webservice',
  principal    => 'SCOTT',
  is_grant     => TRUE,
  privilege    => 'connect');
END;
/

-- Step 2: Assign the Access Control List to One or More Network Hosts
-- After you create the access control list, then you are ready to assign it to one or more network host computers.
BEGIN
DBMS_NETWORK_ACL_ADMIN.ASSIGN_ACL (
  acl         => 'my_acl.xml',
  host        => '*');
END;
/

In the code above, there is no restrictions on which ports to use. If desirable, use the lower_port and upper_port directives in the ASSIGN_ACL procedure. You can also assign the ACL to apply to one specific host, or group of hosts.

For example

BEGIN
DBMS_NETWORK_ACL_ADMIN.ASSIGN_ACL (
  acl         => 'my_acl.xml',
  host        => 'appserver1.mycompany.com',
  lower_port => 80,
  upper_port => 3999);
END;
/

You can find information about the currently set up ACLs in the following views:

DBA_NETWORK_ACLS

DBA_NETWORK_ACL_PRIVILEGES

DBA_WALLET_ACLS

USER_NETWORK_ACL_PRIVILEGES

Sources: Oracle Documentation

http://docs.oracle.com/cd/E11882_01/network.112/e36292/authorization.htm#DBSEG121 - creating an ACL
http://docs.oracle.com/cd/E11882_01/network.112/e36292/authorization.htm#DBSEG99984 - finding information about ACL
http://docs.oracle.com/cd/E11882_01/network.112/e36292/authorization.htm#DBSEG106 - Specifying a Group of Network Host