RFC 3612 (rfc3612) - Page 2 of 16

Applicability Statement for Restart Mechanisms for the Label Distribution Protocol (LDP)

RFC 3612        Applicability for LDP Restart Mechanisms  September 2003


2.  Requirements of an LDP FT System

   Many MPLS LSRs may exploit FT hardware or software to provide high
   availability (HA) of core networks.  In order to provide HA, an MPLS
   system needs to be able to survive a variety of faults with minimal
   disruption to the Data Plane, including the following fault types:

   -  failure/hot-swap of the switching fabric in an LSR,

   -  failure/hot-swap of a physical connection between LSRs,

   -  failure of the TCP or LDP stack in an LSR,

   -  software upgrade to the TCP or LDP stacks in an LSR.

   The first two examples of faults listed above may be confined to the
   Data Plane.  Such faults can be handled by providing redundancy in
   the Data Plane which is transparent to LDP operating in the Control
   Plane.  However, the failure of the switching fabric or a physical
   link may have repercussions in the Control Plane since signaling may
   be disrupted.

   The third example may be caused by a variety of events including
   processor or other hardware failure, and software failure.

   Any of the last three examples may impact the Control Plane and will
   require action in the Control Plane to recover.  Such action should
   be designed to avoid disrupting traffic in the Data Plane.  Since
   many recent router architectures can separate the Control and Data
   Planes, it is possible that forwarding can continue unaffected by
   recovery action in the Control Plane.

   In other scenarios, the Data and Control Planes may be impacted by a
   fault, but the needs of HA require the coordinated recovery of the
   Data and Control Planes to a state that existed before the fault.

   The provision of protection paths for MPLS LSP and the protection of
   links, IP routes or tunnels through the use of protection LSPs is
   outside the scope of this document.  See [RFC 3469] for further
   information.

3.  General Considerations

   In order for the Data and Control Plane states to be successfully
   recovered after a fault, procedures are required to ensure that the
   state held on a pair of LDP peers (at least one of which was affected





Farrel                       Informational