Juniper JUNOSE, Configuration Manual

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Use the no version to delete the set clause from a route map.
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See set metric.
Missing MED Values
By default, a route that arrives with no MED value is treated as if it had a MED of 0,
the most preferred value. You can use the
bgp bestpath missing-as-worst command
to specify that a route with any MED value is always preferred to a route that is
missing the MED value.
bgp bestpath missing-as-worst
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Use to set a missing MED value to infinity, the least preferred value.
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After issuing this command, a route missing the MED is always preferred less
than any route that has a MED configured.
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Example
host1(config-router)# bgp bestpath missing-as-worst
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Changes apply automatically whenever BGP subsequently runs the best-path
decision process for a destination prefix; that is, whenever a best route is picked
for a given prefix.
To force BGP to run the decision process on routes already received, you must
use the
clear ip bgp command to perform an inbound soft clear or hard clear
of the current BGP session.
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Use the no version to restore the default condition, where a missing MED value
is set to 0, the most preferred value.
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See bgp bestpath missing-as-worst.
Comparing MED Values Within a Confederation
A BGP speaker within a confederation of sub-ASs might need to compare routes to
determine the best path to a destination. By default, BGP does not use the MED value
when comparing routes originated in different sub-ASs within the confederation to
which the BGP speaker belongs. (Within the confederation, routes learned from
different sub-ASs are treated as having originated in different places.) You can use
the
bgp bestpath med confed command to force MED values to be taken into account
within a confederation.
bgp bestpath med confed
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Use to specify that BGP take into account the MED when comparing routes
originated in different sub-ASs within the confederation to which the BGP speaker
belongs.
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This command does not affect the comparison of routes that are originated in
other ASs and does not affect the comparison of routes that are originated in
other confederations.
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Example
Selecting the Best Path
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Chapter 1: Configuring BGP Routing