Appendix A: Changes to [RFC6325] and Interoperability Considerations

   This appendix summarizes the significant changes this document
   makes to the TRILL base protocol specification [RFC6325].  Although
   simultaneous use of [RFC6325] ESADI and ESADI as specified in this
   document in a TRILL campus is very unlikely due to non-deployment
   of [RFC6325] ESADI, this Appendix also discusses, for each change,
   the interoperability considerations should such simultaneous use
   occur.

A.1 ESADI PDU Changes

   The format of ESADI-LSP, ESADI-CSNP, and ESADI-PSNP PDU payloads is
   changed from the IS-IS Level 1 format [IS-IS] to the Extended Level
   1 Circuit Scoped format (E-L1CS) specified in [FS-LSP]. This change
   is not backwards compatible with [RFC6325]. It is made in light of
   the 256 times greater information carrying capacity of the E- L1CS
   format compared with the base IS-IS format. It is anticipated that
   this greater carrying capacity will be needed, under some
   circumstances, to carry end station addressing information or other
   information that is added to ESADI in the future.

   The PDU numbers used for the ESADI LSP, CSNP, and PSNP PDUs in
   [RFC6325] are 18, 24, and 26 [IS-IS]. With this document, the
   format changes and the PDU numbers change to 10, 11, and 12
   [FS-LSP].  The use of different PDU numbers assures that a PDU will
   not be mis-parsed.  Because of this, implementations of this
   document and implementations of [RFC6325] ESADI will discard each
   other's PDUs. Thus address reachability or other information
   distributed through either type of ESADI implementation will only
   be communicated to other implementations of the same type and the
   two communities will not communicate any information with each
   other.

   Note that RBridges can use the TRILL mandatory-to-implement,
   enabled-by-default data plane address learning in addition to
   ESADI. (Section 5 of this document and the material it references
   explain how to handle conflicts between different sources of
   address reachability information.) Simply leaving data plane
   address learning enabled would enable smooth migration from
   [RFC6325] EASDI to the ESADI specification in this document, should
   that be necessary. The data plane address learning would fill in
   any gaps due to non-communication between the two types of ESADI
   implementation although without the speed or security advantages of
   ESADI.

A.2 Unicasting Changes

   Unicasting of ESADI PDUs is optionally supported including
   replacing Section 4.6.2.2 of [RFC6325] with the new text give in
   Section 4.1 of this document. This unicast support is backwards
   compatible because it is only used when the recipient RBridge
   signals its support.

A.3 Message Timing Changes and Suggestions

   The following timing relevant ESADI message changes and suggestions
   are included in this document:

   1. Provide for staggered delay for non-originators of ESADI-LSP
      fragments in response to requests for such fragments by CSNP and
      PSNP messages.

   2. Suggest staggered timing of unicast ESADI-LSPs when a new ESADI
      RBridge appears on the EASDI virtual link.

   These relate only to the timing of messages for congestion
   minimization.  Should a message be lost due to congestion, it will
   be later retransmitted as a normal part of the robust flooding
   mechanism used by ESADI.

A.4 Duplicate Address Reachability

   The handling of persistent reachability of the same MAC within the
   same Data Label from two or more RBridge is substantially modified
   including the explicit replacement of some text in Section 4.2.6 of
   [RFC6325] (see Section 5.3 of this document). There is no problem
   with a mixture of ESADI implementations in a TRILL campus, some
   conforming to [RFC6325] and some conforming with this document, for
   handling this condition. The more implementations conform to the
   improved behavior specified in this document for this condition,
   the better the traffic spreading will be and the less likely
   address flip-flopping problems are.