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Routing & Switching · Advanced

OSPF Down Bit

A flag a PE sets in Type 3/5/7 LSAs sent to a CE so other PEs will not redistribute them back into MP-BGP.

Definition

The down bit prevents routing loops at multihomed sites running OSPF as the PE-CE protocol. A VRF-Lite CE may need capability vrf-lite to ignore the down bit.

Example

capability vrf-lite under router ospf 1 vrf X on a multi-VRF CE

Exam tip

Routes missing on a VRF-Lite CE running OSPF often trace back to the down bit.

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