In scenarios where network configuration information related to IPv6
   prefixes becomes invalid without any explicit and reliable signaling
   of that condition (such as when a Customer Edge router crashes and
   reboots without knowledge of the previously employed prefixes), hosts
   on the local network may continue using stale prefixes for an
   unacceptably long time (on the order of several days), thus resulting
   in connectivity problems.  This document describes this issue and
   discusses operational workarounds that may help to improve network
   robustness.  Additionally, it highlights areas where further work may
   be needed.