HP 3600 v2 series Configuration Manual page 207

Figure 78 MED attribute
2.1.1.1
D = 9.0.0.0
Next_hop = 2.1.1.1
MED = 0
EBGP
Router A
EBGP
D = 9.0.0.0
Next_hop = 3.1.1.1
MED = 100
3.1.1.1
AS 10
In general, BGP compares MEDs of routes received from the same AS only.
NOTE:
The current implementation supports using the compare-different-as-med command to force BGP to
compare MED values of routes received from different ASs.
LOCAL_PREF
5.
The LOCAL_PREF attribute is exchanged between iBGP peers only; therefore, it is not advertised to any
other AS. It indicates the priority of a BGP router.
LOCAL_PREF is used 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
from AS20 to AS10 travels through Router C that is selected according to LOCAL_PREF.
Figure 79 LOCAL_PREF attribute
COMMUNITY
6.
The COMMUNITY attribute is a group of specific data. A route can carry one or more COMMUNITY
attribute values (each of which is represented by a four-byte integer). The receiving router processes the
route (for example, determining whether to advertise the route and the scope for advertising the route)
MED = 0
Router B
IBGP
Router D
IBGP
IBGP
Router C
AS 20
MED = 100
195
9.0.0.0
Figure 79, traffic