RFC 2097

Network Working Group                                            G. Pall
Request for Comments: 2097                               Microsoft Corp.
Category: Standards Track                                   January 1997

            The PPP NetBIOS Frames Control Protocol (NBFCP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.  PPP
   defines an extensible Link Control Protocol, and proposes a family of
   Network Control Protocols for establishing and configuring different
   network-layer protocols.

   The NBF protocol [3] was originally called the NetBEUI protocol. This
   document defines the Network Control Protocol for establishing and
   configuring the NBF protocol over PPP.

   The NBFCP protocol is only applicable for an end system to connect to
   a peer system or the LAN that peer system is connected to.  It is not
   applicable for connecting two LANs together due to NetBIOS name
   limitations and NetBIOS name defense mechanisms.

Table of Contents

   1.     Introduction ..........................................    2
      1.1       Specification of Requirements ...................    2
      1.2       Terminology .....................................    3
   2.     A PPP Network Control Protocol for NBF ................    3
      2.1       Sending NBF Datagrams ...........................    4
      2.2       Bridging NBF Datagrams...........................    5
      2.3       NetBIOS Name Defense.............................    5
   3.     NBFCP Configuration Options ...........................    6
      3.1       Name-Projection..................................    6
      3.2       Peer-Information.................................    8
      3.3       Multicast-Filtering..............................   10
      3.4       IEEE-MAC-Address-Required........................   11
   SECURITY CONSIDERATIONS ......................................   12
   REFERENCES ...................................................   12

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RFC 2097                         NBFCP                      January 1997

   ACKNOWLEDGEMENTS .............................................   13
   CHAIR'S ADDRESS ..............................................   13
   AUTHOR'S ADDRESS .............................................   13

1.  Introduction

   PPP has three main components:

      1. A method for encapsulating multi-protocol datagrams.

      2. A Link Control Protocol (LCP) for establishing, configuring,
         and testing the data-link connection.

      3. A family of Network Control Protocols for establishing and
         configuring different network-layer protocols.

   In order to establish communications over a point-to-point link, each
   end of the PPP link must first send LCP packets to configure and test
   the data link.  After the link has been established and optional
   facilities have been negotiated as needed by the LCP, PPP must send
   NBFCP packets to choose and configure the NBF network-layer protocol.
   Once NBFCP has reached the Opened state, NBF datagrams can be sent
   over the link.

   The link will remain configured for communications until explicit LCP
   or NBFCP packets close the link down, or until some external event
   occurs (an inactivity timer expires or network administrator

1.1.  Specification of Requirements

   In this document, several words are used to signify the requirements
   of the specification.  These words are often capitalized.

   MUST      This word, or the adjective "required", means that the
             definition is an absolute requirement of the specification.

   MUST NOT  This phrase means that the definition is an absolute
             prohibition of the specification.

   SHOULD    This word, or the adjective "recommended", means that there
             may exist valid reasons in particular circumstances to
             ignore this item, but the full implications should be
             understood and carefully weighed before choosing a
             different course.

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RFC 2097                         NBFCP                      January 1997

   MAY       This word, or the adjective "optional", means that this
             item is one of an allowed set of alternatives.  An
             implementation which does not include this option MUST be
             prepared to interoperate with another implementation which
             does include the option.

1.2.  Terminology

   This document frequently uses the following terms:

   peer      The other end of the point-to-point link.

   silently discard
            This means the implementation discards the packet without
            further processing.  The implementation SHOULD provide the
            capability of logging the error, including the contents of
            the silently discarded packet, and SHOULD record the event
            in a statistics counter.

            A user's machine.  It only sends packets to servers and
            other end-systems.  It doesn't pass any packets through

   router    Allows packets to pass through, usually from one ethernet
             segment to another.  Sometimes these are called

   bridge    Allows packets to pass through with the data field
             unmodified.  Usually from one ethernet segment to another
             or from one ethernet segment to a token-ring segment.

   gateway   Allows packets to be sent from one network protocol to
             the same or different network protocol.  For example,
             NetBIOS packets from an NBF network to a TCP/IP network
             which has implemented RFC 1001 and RFC 1002.

   local access only server A server which does not pass any packets
             through itself to other servers.

2.  A PPP Network Control Protocol for NBF

   The NBF Control Protocol (NBFCP) is responsible for configuring,
   enabling, and disabling the NBF protocol modules on both ends of the
   point-to-point link.  NBFCP uses the same packet exchange mechanism
   as the Link Control Protocol.  NBFCP packets MUST NOT be exchanged
   until PPP has reached the Network-Layer Protocol phase.  NBFCP
   packets received before this phase is reached should be silently

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RFC 2097                         NBFCP                      January 1997


   The NBF Control Protocol is exactly the same as the Link Control
   Protocol [1] with the following exceptions:

   Frame Modifications

      The packet may utilize any modifications to the basic frame format
      which have been negotiated during the Link Establishment phase.

   Data Link Layer Protocol Field

      Exactly one NBFCP packet is encapsulated in the Information field
      of a PPP Data Link Layer frame where the Protocol field indicates
      type hex 803f (NBF Control Protocol).

   Code field

     Only Codes 1 through 7 (Configure-Request, Configure-Ack,
     Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack
     and Code-Reject) are used.  Other Codes should be treated as
     unrecognized and should result in Code-Rejects.


     NBFCP packets MUST NOT be exchanged until PPP has reached the
     Network-Layer Protocol phase.  An implementation should be
     prepared to wait for Authentication and Link Quality Determination
     to finish before timing out waiting for a Configure-Ack or other
     response.  It is suggested that an implementation give up only
     after user intervention or a configurable amount of time.  Also,
     because NetBIOS name defense takes time (typically a minimum of
     3 seconds if names are added in parallel), it is suggested that
     if Name-Projection is negotiated, the timeouts are increased to 10

   Configuration Option Types

     NBFCP has a distinct set of Configuration Options.

2.1.  Sending NBF Datagrams

   Before any NBF packets may be communicated, PPP must reach the
   Network-Layer Protocol phase, and the NBF Control Protocol must reach
   the Opened state.

   Unless otherwise negotiated, exactly one NBF packet is encapsulated
   in the Information field of a PPP Data Link Layer frame where the

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   Protocol field indicates type hex 003f (NBF datagram).

   Since NBF datagrams for PPP do not contain a datagram length field,
   the encapsulated NBF packet MUST NOT contain any extra octet padding
   except when Self-Defining-Padding is negotiated.

   The maximum length of an NBF datagram transmitted over a PPP link is
   the same as the maximum length of the Information field of a PPP data
   link layer frame.  Since there is no standard method for fragmenting
   and reassembling NBF datagrams, PPP links supporting NBF MUST allow
   at least 576 octets in the information field of a data link layer
   frame.  It is recommended that an implementation allow 1500 octets in
   the information field unless the IEEE-MAC-Address-Required boolean
   option is negotiated (see below).

2.2   Bridging NBF Datagrams

   There exist at least four different MAC header implementations for
   NBF packets: 802.3 Ethernet, 802.5 Token-Ring, DIX Ethernet, and
   FDDI.  Because NBF is not a routable protocol, some PPP
   implementations may require IEEE MAC addresses to properly route or
   bridge NBF packets.  Some PPP implementations may require the entire
   MAC media header in order to properly route or bridge NBF packets.
   Other smarter implementations may only require the IEEE MAC addreses,
   and still other implementations (such as NetBIOS gateways) may not
   require any MAC address fields.  NBFCP implementations which require
   IEEE Addresses should negotiate the NBFCP IEEE-MAC-Address-Required
   boolean configuartion option so that the MAC header can be provided
   in the NBF packet.

   If IEEE-MAC-Address-Required boolean configuration option is
   negotiated, all NBF datagrams MUST be sent with the specified 12
   octet IEEE MAC address header.  Since negotiation of this option
   occurs after the LCP phase, NBF packets MAY exceed the negotiated PPP
   MRU size.  A PPP implementation which negotiates this option MUST
   allow reception of PPP NBF packets 12 octets larger than the
   negotiated MRU size.

2.3   NetBIOS Name Defense

   In order to guarantee uniqueness of NetBIOS Names on the network,
   NBFCP requires that end-system implementations MUST negotiate the
   Name-Projection configuration option.

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3.  NBFCP Configuration Options

   NBFCP Configuration Options allow modifications to the standard
   characteristics of the network-layer protocol to be negotiated.  If a
   Configuration Option is not included in a Configure-Request packet,
   the default value for that Configuration Option is assumed.

   NBFCP uses the same Configuration Option format defined for LCP [1],
   with a separate set of Options.

   Up-to-date values of the NBFCP Option Type field are specified in the
   most recent "Assigned Numbers" RFC [2].  Current values are assigned
   as follows:

      1       Name-Projection
      2       Peer-Information
      3       Multicast-Filtering
      4       IEEE-MAC-Address-Required

3.1.  Name-Projection


      This Configuration Option provides a method for the peer to
      provide the NetBIOS names registered on its network.  The sender
      of the Configure-Request states which NetBIOS names should be
      added by the remote peer.  More than one Name-Projection option
      MAY appear in a single Configure-Request.

      Implementations which do not attempt to add any NetBIOS names MUST
      Configure-Reject the Name-Projection Configuration Option.

      If the Name-Projection Configuration Option is not offered by the
      remote peer, but is required by the local peer, the local peer
      should Configure-Nak the request and indicate that it wishes the
      remote peer to add zero NetBIOS names because it is the only known
      acceptable value.  The remote peer may then terminate NBFCP,
      attempt to add zero NetBIOS names, or attempt add one or more
      NetBIOS names.

      When the receiving peer cannot add all the requested names, it
      MUST Configure-Nak with the complete list of names requested.
      Those names which could be added should have the Added field set
      to zero. Those names which could not be added should have the
      Added field set to an appropriate non-zero return code.  The
      sender of this Configuration Option SHOULD then resend the
      Configure-Request with the successfully added names.

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RFC 2097                         NBFCP                      January 1997

      The implementation may choose to fail configuration if the
      complete list of NetBIOS names is not accepted.  By failing, the
      implementation should terminate NBFCP by sending a Terminate-
      Request packet.

      Because adding NetBIOS names can take time (usually 3 seconds) and
      because PPP may default the restart timer to 3 seconds, the
      restart timer SHOULD default to 10 seconds when configuring
      NetBIOS names.

   A summary of the Name-Projection Configuration Option format is shown
   below.  The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |     Type      |    Length     |      1st NetBIOS-Name
   |   1st NetBIOS-Name (cont.)
   |   1st NetBIOS-Name (cont.)
   |   1st NetBIOS-Name (cont.)
   |   1st NetBIOS-Name (cont.)    |    Added      |2nd NetBIOS Name...




      2 + (Number of NetBIOS names * 17)


      This group of zero or more sixteen octet NetBIOS-Name fields
      contains a list of all the NetBIOS names the peer wishes to add to
      the remote network if the packet is Configure-Request.  If the
      packet is Configure-Reject, the peer does not support this
      configuration option and it can be assumed that no NetBIOS names
      were added.

      Because the length field is only one octet, only 14 NetBIOS names
      can be added per Name-Projection option.  If more than 14 NetBIOS
      names should be added, then more than one Name-Projection option
      packet will have to be sent in the Configure-Request packet.

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RFC 2097                         NBFCP                      January 1997


      This is a one octet field which plays a dual role.  The Added
      field in the Name-Projection Request packet contains the type of
      NetBIOS name added.  A summary of name types is listed below.

         01   Unique Name.
         02   Group Name.

      If the packet is a Configure-Reject the Added field should contain
      the NetBIOS return code for the NetBIOS Add Name or NetBIOS Add
      Group Name command as defined in the NetBIOS 3.0 specification =

   A summary of common result codes is listed below in type hex.

         00   Name successfully added.
         0D   Duplicate name in local name table.
         0E   Name table full.
         15   Name not found or cannot specify "*" or null.
         16   Name in use on remote NetBIOS.
         19   Name conflict detected.
         30   Name defined by another environment.
         35   Required system resources exhausted.

3.2.  Peer-Information


      This Configuration Option provides a way for the peer to
      communicate NetBIOS pertinent configuration information. Although
      negotiation of this option is not mandatory, it is suggested.

   A summary of the Peer-Information Option format is shown below.  The
   fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |     Type      |    Length     |         Peer-class            |
   |        Peer-version (major)   |       Peer-version(minor)    |
   |        Peer-name ....

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      If the length is 8, there is no Peer-name.  If the length is
      greater than 8, the Peer-name's length is Length - 8.


      The Peer-class field is one octet. It identifies the sender's
      implementation type.

      Initial values are assigned as follows:

      Value           Class

        1             Reserved for legacy implementations.
        2             PPP NetBIOS Gateway Server.
        3             Reserved for legacy implementations.
        4             PPP Local Access Only Server.
        5             Reserved for legacy implementations.
        6             PPP NBF Bridge.
        7             Reserved for legacy implementations.
        8             PPP End-System.


      The Peer-version field is four octets and indicates the version of
      the communication peer providing one side of the PPP connection.
      The first two octets are the major version number and the last two
      octets are the minor version number.  The major and minor version
      represent a 16 bit unsigned number sent with the most significant
      octet first.


      The name of the peer.  A suggested name is the NetBIOS workstation
      name of the peer.  If the length field is 8, no peer name is
      provided.  The peer-name may not be greater than 32 octets in

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RFC 2097                         NBFCP                      January 1997

3.3.  Multicast-Filtering


      This Configuration Option provides a way to negotiate the use of
      the Multicast-Forward-Period and the Multicast-Priority.  This
      Configuration Option provides a way to negotiate how to handle
      mulicast packets.  It allows the sender of the Configure-Request
      to state the current handling of multicast packets.  The peer can
      request parameters by NAKing the option, and returning valid
      Multicast-Filtering parameters.

      If negotiation about the remote Multicast-Filtering is required,
      and the peer did not provide the option in its Configure-Request,
      the option SHOULD be appended to a Configure-Nak.

      Controlling the multicast rate is important because some NetBIOS
      applications use multicasts to communicate and withholding
      multicasts may prevent these applications from working.  It is
      also true that other NetBIOS applications do not need to receive
      any multicast packets and therefore it is best to quench the rate
      at which the peer will send multicast packets.

      By default, the peer is pre-configured to an administrator
      assigned Multicast-Forward-Period and Priority.  A Multicast-
      Forward-Period specified as hex type FFFF in a Configure-Request
      is interpreted as requesting the receiving peer to specify a value
      in its Configure-Nak.  A Multicast-Forward-Period value specified
      as hex type FFFF in a Configure-Nak is interpreted as agreement
      that no value exists. A Multicast-Forward-Period of zero indicates
      that all multicast packets SHOULD be forwarded.

      Peers that rely on all multicast packets being forwarded SHOULD
      request a Multicast-Forward-Period of zero and a Multicast-
      Priority of one by NAKing the Configure-Request option and
      appending the proper parameters to a Configure-Nak.

   A summary of the Multicast-Filtering Configuration Option format is
   shown below.  The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |     Type      |    Length     |    Multicast-Forward-Period   |
   |   Priority    |

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RFC 2097                         NBFCP                      January 1997






      The Multicast-Forward-Period field is two octets and indicates
      the maximum period in seconds at which multicast packets can
      be sent.  The maximum value for this field is 60 (one minute).
      A value of zero indicates that there is no maximum period at
      which multicast packets can be sent.  A value of hex type FFFF
      indicates that the Multicast-Forward-Period is unknown.  A value
      of five indicates that multicast packets will not be sent at a
      rate more frequent than once every five seconds.  This two
      octet value represents a 16 bit unsigned number sent with
      the most significant octet first.


      The Priority field is one octet long and indicates if multicast
      packets have priority over other packets when being sent.  A value
      of 0 indicates that directed packets have priority.  A value of 1
      indicates that multicast packets have priority.

3.4.  IEEE-MAC-Address-Required


      This boolean Configuration Option provides a method for the peer
      to require that all NBF datagrams be sent with a 12 octet IEEE MAC
      Address header.  By default, it is assumed that no MAC header is

   A summary of the IEEE-MAC-Address-Required Boolean Configuration
   Option format is shown below.  The fields are transmitted from left
   to right.

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   |     Type      |    Length     |

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RFC 2097                         NBFCP                      January 1997






      By default the NBF datagram is sent without any MAC header
      information.  The NBF datagram information field is equivalent to
      the data field in 802.3, 802.5, and FDDI frames.

      If this option is negotiated successfully, each NBF datagram is
      sent with a 12 octet IEEE MAC Address header prepended to the
      information field.  A summary of the information field when using
      12 octet IEEE MAC Headers is shown below. The fields are
      transmitted from left to right.  The MAC Address is in non-
      canonical form. This means that the first bit to be transmitted in
      every byte is the most significant bit.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |                       Destination MAC Address                 |
   |     Destination MAC Address   |  Source MAC Address           |
   |                       Source MAC Address                      |
   |               802.3/802.5/FDDI data field...

Security Considerations

   Security issues are not discussed in this memo.


   [1]   Simpson, W., Editor, "The Point-to-Point Protocol (PPP)",
         STD 51, RFC 1661, July 1994.

   [2]   Reynolds, J., and J. Postel, "Assigned Numbers", STD 2,
         RFC 1700, October 1994.

   [3]   IBM Corp., "IBM Local Area Network Technical Reference",
         Third Edition, Document Number SC30-3383-2, November 4, 1988.

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RFC 2097                         NBFCP                      January 1997

   [4]   Baker, F., and R. Bowen "PPP Bridging Control Protocol (BCP)",
         Work in Progress.


   Some of the text in this document is taken from previous documents
   produced by the Point-to-Point Protocol Working Group of the Internet
   Engineering Task Force (IETF).

   Thomas J. Dimitri (previously at Microsoft Corporation) authored the
   original draft.

   Special thanks go to coworkers at Microsoft, Bill Simpson
   (Daydreamer), Tom Coradetti (DigiBoard), Marty Del Vecchio (Shiva),
   Russ Gocht (Shiva) and several members of the IETF PPP Working Group.

Chair's Address

   The working group can be contacted via the current chair:

      Karl Fox
      Ascend Communications
      3518 Riverside Drive, Suite 101
      Columbus, Ohio 43221


Author's Address

   Questions about this memo can also be directed to:

      Gurdeep Singh Pall
      Microsoft Corporation
      1 Microsoft Way
      Redmond, WA 98052-6399

      EMail: gurdeep@microsoft.com

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