| RFC 8978 | Reaction to Renumbering Events | December 2020 |
| Gont, et al. | Informational | [Page] |
In scenarios where network configuration informationrelated to IPv6 prefixes becomes invalid without any explicit and reliablesignaling of that condition (such as when a Customer Edge router crashes andreboots without knowledge of the previously employed prefixes), nodes on thelocal network may continue using stale prefixes for an unacceptably long time(on the order of several days), thus resulting in connectivity problems. Thisdocument describes this issue and discusses operational workarounds that mayhelp to improve network robustness. Additionally, it highlights areas wherefurther work may be needed.¶
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IPv6 Stateless Address Autoconfiguration (SLAAC)[RFC4862] conveys information about prefixes to beemployed for address configuration via Prefix Information Options (PIOs) sentin Router Advertisement (RA) messages. IPv6 largely assumes prefix stability,with network renumbering only taking place in a planned manner, old/staleprefixes being phased out via reduced prefix lifetimes, and new prefixes (withlonger lifetimes) being introduced at the same time. However, there are severalscenarios that may lead to the so-called "flash-renumbering" events, where theprefix employed by a network suddenly becomes invalid and replaced by a newprefix. In some of these scenarios, the local router producing the networkrenumbering event may try to deprecate the currently employed prefixes (byexplicitly signaling the network about the renumbering event), whereas in otherscenarios, it may be unable to do so.¶
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For a number of reasons (such as the ones stated above), IPv6 deployments may employ dynamic prefixes (even at the expense of the issues discussed in this document), and there might be scenarios in which the dynamics of a network are such that the network exhibits the behavior of dynamic prefixes. Rather than trying to regulate how operators may run their networks, this document aims at improving network robustness in the deployed Internet.¶