Missing Med Values; Comparing Med Values Within A Confederation - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

JunosE 11.3.x BGP and MPLS Configuration Guide
bgp bestpath missing-as-worst
bgp bestpath med confed
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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.
Use to set a missing MED value to infinity, the least preferred value.
After issuing this command, a route missing the MED is always preferred less than any
route that has a MED configured.
Example
host1(config-router)#bgp bestpath missing-as-worst
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.
Use the no version to restore the default condition, where a missing MED value is set
to 0, the most preferred value.
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.
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.
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.
Example
host1(config-router)#bgp bestpath med confed
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.
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