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Routing & Switching · Intermediate

Multi-Exit Discriminator (MED)

An optional non-transitive BGP attribute that suggests to a neighboring AS which entry point to use; lower is preferred.

Definition

MED is sent to eBGP neighbors and propagated inside their AS but not beyond. By default it is compared only between paths from the same neighboring AS (always-compare-med changes that). A missing MED is treated as 0 on Cisco unless bgp bestpath med missing-as-worst is set.

Example

route-map TO-ISP permit 10 / set metric 50

Exam tip

MED is a hint to a neighbor AS and is weaker than local preference and AS path length.

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