H3C Technologies H3C SR8800 - Manual (Page 236)

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Configuring the MED attribute
MED is used to determine the best route for traffic going into an AS. When a BGP router obtains from
EBGP peers multiple routes to the same destination but with different next hops, it considers the route with
the smallest MED value as the best route if other conditions are the same.
Configuring the default MED value
To configure the default MED value:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter BGP view. bgp as-number N/A
3. Configure the default MED value. default med med-value
Optional
0 by default
Enabling the comparison of MED of routes from different ASs
To enable the comparison of MED of routes from different ASs:
Step Command Remarks
1. Enter system view. system-view N/A
2. Enter BGP view. bgp as-number N/A
3. Enable the comparison of MED of
routes from different ASs.
compare-different-as-med Not enabled by default
Enabling the comparison of MED of routes from each AS
Route learning sequence may affect optimal route selection.
Figure 86 Route selection based on MED
As shown in Figure 86 , Router D learns network 10.0.0.0 from both Router A and Router B. Because
Router B has a smaller router ID, the route learned from it is optimal.
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.0.0.0 2.2.2.2 50 0 300e
* i 3.3.3.3 50 0 200e
AS
AS 300
AS 100
AS 200
Router A
Router D
Router ID: 3.3.3.3
Router C Router B
GE3/1/0
2.2.2.2/24
Router ID: 1.1.1.1 Router ID: 2.2.2.2
1.1.1.1/24
GE3/1/0
3.3.3.3/24
GE3/1/0