+------------+                               +-------------+             |                                            |             |                                            |             |                                            |             |                                            |             |    +---------------------------------+     |             |    |          FTP  -  FTAM           |     |             |    |       Gateway Application       |     |             |    |---------------------------------|     |             |    |      FTP       |      FTAM      |     |             |    |----------------+----------------|     |             |    |    TCP/IP      |    TP4/et al   |     |             |    +---------------------------------+     |             |           /|\               /|\            |             |            |                 |             |             +------------+                 +-------------+                  Figure 3  -  Gateway Protocol Stack   A fundamental aspect of this gateway architecture is that data is   mapped and transmitted immediately; i.e., no transferred file need   ever reside on the gateway file system.  In the context of this   document, the term "filesystem" refers to the file access and   maintenance mechanisms provided by the operating system.  This lack   of gateway filesystem interaction helps speed up the end-to-end data   transfer.  Another speed-enhancing feature of this architecture is   that both the FTP and FTAM network connections can operateMindel & Slaski                                                 [Page 7]RFC 1415             FTP-FTAM Gateway Specification         January 1993   simultaneously.  Additional advantages include:        1. FTP and FTAM hosts require no modification to utilize gateway           services.        2. Users require no knowledge of the other protocol.        3. Gateway access control is not impaired (since users cannot           directly access the gateway filesystem).        4. No additional filesystem space is required on the gateway.        5. Interactive nature of protocols is preserved.        6. Users become aware of fatal errors immediately.   Disadvantages of this design include the initial coding effort   required to develop the gateway and the subsequent re-coding efforts   required to keep it current.3. Network Naming and Addressing   The network naming and addressing schemes used by FTP (Domain Names   (DN), IP Addresses) and FTAM (Distinguished Names, Presentation   Addresses) are quite different.  This issue is quite apparent when a   user of one protocol needs to identify a destination host of the   other protocol.   In the TCP/IP naming and addressing scheme, the identity of the FTP   Server is its DN and its IP address [RFC1101].  To initiate a   connection to an FTP Server, the FTP Client looks up a DN in either   the Domain Name System (DNS) or static host table and obtains an IP   address.   In the OSI naming and addressing scheme, the identity of the FTAM   Responder service is its Distinguished Name in the OSI Directory   (X.500 or static table) and its Presentation address.  The   Distinguished Name is an authoritative description of the service.  A   Presentation address consists of a Presentation selector, a session   selector, a transport selector, and a network address.  To initiate a   connection to an FTAM Responder, the FTAM Initiator contacts the OSI   Directory, presents the Distinguished Name of the desired FTAM   Responder and asks for the Presentation address attribute associated   with that name.   An alternative to the direct use of Distinguished Names is to use   "User Friendly Naming", as defined in [Kille92].  Gateway support for   "User Friendly Naming" is recommended, but not required.Mindel & Slaski                                                 [Page 8]RFC 1415             FTP-FTAM Gateway Specification         January 19934. Use of the Gateway Services4.1. FTP-Initiated Gateway Service   The FTP Client uses the FTP-Initiated gateway service to utilize the   resources of an FTAM Responder.   To initiate a file transfer from an FTP Client, the Client connects   to the FTP-Initiated gateway service via TCP/IP.  The gateway then   establishes a connection, via OSI, to the FTAM Responder.  At this   point, the user can initiate file transfer operations.   The FTP Client is responsible for providing the gateway with an   authoritative Distinguished Name, or a User Friendly Name, of the   desired OSI filestore.  It is the responsibility of the gateway to   resolve this Distinguished Name, or User Friendly Name, to its   corresponding Presentation address.   The logon sequence taken by an FTP Client when initiating a file   transfer with an FTAM Responder is given below:             % ftp gateway             ftp> site Distinguished-Name-of-FTAM Responder             ftp> user username             ftp> pass password   The "ftp gateway" command initiates the connection between the FTP   Client and the gateway.  Once connected to the gateway, the FTP   Client should identify the desired FTAM Responder service via the   Responder's Distinguished Name, or User Friendly Name, which is   resolved by an algorithm running on the Directory Services provider.   This information is sent via a "site Distinguished-Name-of-FTAM   Responder" or "site UFN-of-FTAM Responder" command.   Upon receipt of a Distinguished Name or a User Friendly Name, it is   the gateway's responsibility to resolve it to the Presentation   Address associated with that name.  This resolution is done by   contacting the OSI Directory (X.500 or local static table) and   presenting the Distinguished Name or User Friendly Name.  Once the   Presentation address is obtained, the gateway can attempt a   connection with the ultimate destination file transfer service   represented by this Presentation address.   The userid is passed via the "user username" command, and the   password is passed via the "pass password".  If the FTAM Responder   requires a password, a password prompt should appear after issuing   the "user username" command.  It is anticipated that stronger   authentication mechanisms will be required for DoD gateways in theMindel & Slaski                                                 [Page 9]RFC 1415             FTP-FTAM Gateway Specification         January 1993   future.   Using a specific example, suppose an FTAM Responder has the following   Distinguished Name:           CountryName          =         "US"           Organization         =         "Open Networks"           OrganizationalUnit   =         "Network Services"           CommonName           =         "netwrx1"           CommonName           =         "FTAM service"   and the FTP-FTAM gateway is available at "washdc1-osigw.navy.mil".   The FTP user action will appear as:           % ftp washdc1-osigw.navy.mil           ftp> site "c=US@o=Open Networks@ou=Network Services@cn=netwrx1                @cn=FTAM service"           ftp> user mindel           ftp> pass ***********   The "ftp washdc1-osigw.navy.mil" command initiates the connection   between the FTP Client and the FTP-FTAM gateway at the Washington   Navy Yard, Washington D.C.  Once connected, the OSI filestore at Open   Networks is identified via its Distinguished Name, "@c=US@o=Open   Networks@ou=Network Services@cn=netwrx1@cn=FTAM service".   Alternatively, a User Friendly Name, such as:           "netwrx1, Open Networks, us"   can be specified, enabling the following FTP user action:           % ftp washdc1-osigw.navy.mil           ftp> site "netwrx1, Open Networks, us"           ftp> user mindel           ftp> pass ***********   As this example indicates, use of an intermediate gateway is not   transparent.  To partially alleviate this awkwardness, the gateway   can be made more transparent through the registration of the FTAM   host in the DNS using the address of the gateway [RFC1279].   An example will clarify this point.  Suppose that the "netwrx1, Open   Networks, us" FTAM host is registered in the TCP/IP DNS with the DN   of "ftam-service.netwrx1.com" and the IP address of the "washdc1-   osigw.navy.mil" gateway.  In this example, the following set of user   actions is required:Mindel & Slaski                                                [Page 10]RFC 1415             FTP-FTAM Gateway Specification         January 1993           % ftp ftam-service.netwrx1.com           ftp> user mindel           ftp> pass ***********   Since the "ftam-service.netwrx1.com" really points to the gateway   address, the first command will connect the FTP Client to the   gateway.  The gateway will then use the name (using [RFC1279]) to   determine where the actual FTAM host is resident.  Gateway support   for RFC1279 is recommended, but not required.4.2. FTAM-Initiated Gateway Service   The FTAM Initiator uses the FTAM-Initiated gateway service to utilize   the resources of an FTP Server.   To initiate a file transfer from an FTAM Initiator, the Initiator   connects to the FTAM-Initiated gateway service via OSI.  The gateway   then establishes a connection, via TCP/IP, to the FTP Server.  At   this point, the user can initiate file transfer operations.   The FTAM Initiator is responsible for providing the gateway with an   authoritative DN of the desired TCP/IP filestore.  It is the   responsibility of the gateway to resolve this DN to its corresponding   IP address.   The logon sequence taken by an FTAM Initiator when initiating a file   transfer with an FTP Server is given below:           % ftam gateway           ftam> user username@DNS-string           ftam> pass password   The "ftam gateway" command initiates the connection between the FTAM   Initiator and the gateway.  Once connected, userid and TCP/IP   filestore are identified in the "username@DNS-string" argument to the   user command.  If the FTP Server requires a password, a password   prompt should appear after issuing the user command.   The gateway should incorporate the BIND Resolver functionality so   that upon receipt of a Domain Name, the Gateway FTP Client can   resolve it via the distributed Domain Name System.   Using a specific example, suppose that a FTP Server has the following   Domain Name:  "ftp-service.netwrx1.com" and an FTP-FTAM gateway is   available at:Mindel & Slaski                                                [Page 11]RFC 1415             FTP-FTAM Gateway Specification         January 1993           CountryName          =         "US"           Organization         =         "GOV"           OrganizationalUnit   =         "DOD"           OrganizationalUnit   =         "DISA"           Locality             =         "Washington Navy Yard"           CommonName           =         "wnyosi7"   The FTAM user action will appear as:           % ftam @c=US@o=GOV@ou=DOD@ou=DISA@l=Washington Navy Yard                  @cn=wnyosi7           ftam> user mindel@ftp-service.netwrx1.com           ftam> pass ***********   Alternatively, a User Friendly Name could be used rather than the   Distinguished Name.   As mentioned in the previous section, "Use of the FTP-Initiated   Gateway Service", use of an intermediate gateway is not transparent.   The gateway can be made more transparent through the registration of   the FTP host in the X.500 OSI Directory.  By querying the X.500 OSI   Directory, the gateway can identify where the actual host is   resident.   For example, suppose that the FTP Server in the previous example   ("ftp-service.netwrx1.com") is registered in the X.500 Directory with   the following Distinguished Name:           CountryName          =         "US"           Organization         =         "Open Networks"           OrganizationalUnit   =         "Network Services"           CommonName           =         "netwrx1"           CommonName           =         "FTP service"   and the Presentation Address of the FTP-FTAM gateway.  This approach,   described in [RFC1279], would permit the following user interactions:           % ftam @c=US@o=Open Networks@ou=Network Services                  @cn=netwrx1@cn=FTP Service"           ftam> user mindel           ftam> pass ***********4.3. Summary of Usage   As shown in the discussions of the FTP-Initiated and FTAM-Initiated   Gateway Services, the gateway user does not have access to the   gateway filesystem; he merely makes use of the gateway logon   procedure to specify the ultimate destination userid and password.Mindel & Slaski                                                [Page 12]RFC 1415             FTP-FTAM Gateway Specification         January 1993   Two methods of interaction with the gateway were described.  In the   former, the user must:       1. Be aware that a gateway is required to reach the          destination FTP or FTAM host.       2. Determine which gateway is most appropriate for their          respective source-destination pair.       3. Explicitly connect to the gateway host prior to connecting          to the destination host.   Needless to say, the exchange of files between FTP and FTAM hosts   requires more effort than that required for the exchange of files