177
Figure 49 MED attribute
Generally BGP only compares MEDs of routes received from the same AS. You can also use the
compare-different-as-med command to force BGP to compare MED values of routes received from
different ASs.
• LOCAL_PREF
The LOCAL_PREF attribute is exchanged between IBGP peers only, and is not advertised to any
other AS. It indicates the priority of a BGP router.
BGP uses LOCAL_PREF to determine the best route for traffic leaving the local AS. When a BGP
router obtains from several IBGP peers multiple routes to the same destination but with different
next hops, it considers the route with the highest LOCAL_PREF value as the best route. As shown
in Figure 50, traffic from AS 20 to AS 10 travels through R
outer C that is selected according to
LOCAL_PREF.
D = 9.0.0.0
Next_hop = 2.1.1.1
MED = 0
D = 9.0.0.0
Next_hop = 3.1.1.1
MED = 100
MED = 0
Router B
Router A
Router C
Router D
2.1.1.1
3.1.1.1
MED = 100
AS 20
AS 10
9.0.0.0
EBGP
EBGP
IBGP
IBGP
IBGP
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