Consider a BGP free core scenario. Suppose the provider edge BGP
speakers PE1, PE2,..., PEn know about a prefix P/m via the external
routers CE1, CE2,..., CEm. If the PE router PEi loses connectivity to
the primary path, it is desirable to immediately restore traffic by
rerouting packets arriving from the core to PEi and destined to the
prefix P/m to one of the other PE routers that advertised P/m, say PEj,
until BGP re-converges. However if the loss of connectivity of PEi to
the primary path also resulted in the loss of connectivity between PEj
and CEj, rerouting a packet before the control plane converges may
result in a loop. In this document, we propose using a repair label for
traffic restoration while avoiding loops. We propose advertising the
"repair" label through BGP.
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