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connect in two places. Each connection is a BGP session. AS200 sets the MED for its T1 exit point to 100

and the MED for its OC3 exit point to 50. This sets up a path preference through the OC3 link. The MEDs

are advertised to AS100 routers so they know which is the preferred path.

MEDs are non-transitive attributes. If AS100 sends an MED to AS200, AS200 does not pass it on to AS300

or AS400. The MED is a locally relevant attribute to the two participating ASs (AS100 and AS200).

NOTE: The MEDs are advertised across both links, so if a link goes down, AS 1 still has connectivity

to AS300 and AS400.

Figure 26. Multi-Exit Discriminators

NOTE: Configuring the set metric-type internal command in a route-map advertises the

IGP cost as MED to outbound EBGP peers when redistributing routes. The configured set metric

value overwrites the default IGP cost. If the outbound route-map uses MED, it overwrites IGP MED.

Origin

The origin indicates the origin of the prefix, or how the prefix came into BGP. There are three origin

codes: IGP, EGP, INCOMPLETE.

Indicates the prefix originated from information learned through an interior

gateway protocol.

Indicates the prefix originated from information learned from an EGP protocol,

which NGP replaced.

Indicates that the prefix originated from an unknown source.

Generally, an IGP indicator means that the route was derived inside the originating AS. EGP generally

means that a route was learned from an external gateway protocol. An INCOMPLETE origin code

generally results from aggregation, redistribution, or other indirect ways of installing routes into BGP.

Border Gateway Protocol IPv4 (BGPv4)

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