RFC 2043 (rfc2043) - Page 4 of 7

The PPP SNA Control Protocol (SNACP)

RFC 2043                       PPP SNACP                    October 1996


   NLP       Network Layer Packet.  In High Performance Routing (HPR),
             the message unit used to carry data over the route.
             Network Layer Packet is analogous to datagram.

2.  A PPP Network Control Protocol for SNA

   The SNA Control Protocol (SNACP) is responsible for configuring,
   enabling, and disabling SNA on both ends of the point-to-point link.
   SNACP uses the same packet exchange mechanism as the Link Control
   Protocol (LCP). SNACP packets may not be exchanged until PPP has
   reached the Network-Layer Protocol phase.  SNACP packets received
   before this phase is reached should be silently discarded.

   Note that there are actually two SNA Network Control Protocols; one
   for SNA over LLC 802.2 and another for SNA without LLC 802.2.  These
   SNA NCPs are negotiated separately and independently of each other.

   The SNA 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 SNACP packet is encapsulated in the PPP Information
      field, where the PPP Protocol field indicates type hex 804B (SNA
      over LLC 802.2) or hex 804D (SNA).

   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.

   Timeouts

      SNACP packets may 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.





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