HP 6125XLG Configuration Manual page 208

Step
3. Enter BGP IPv6 unicast
instance view.
4. Enable MED comparison for
routes from different ASs.
Enabling MED comparison for routes on a per-AS basis
This task enables BGP to compare the MEDs of routes from an AS.
Figure 53 Route selection based on MED (in an IPv4 network)
AS 200
Router ID : 3.3.3.3
Router A
As shown in
Router B has a smaller router ID, the route learned from Router B is optimal.
Network
*>i 10.0.0.0
* i
When Router D learns network 10.0.0.0 from Router C, it compares the route with the optimal route in its
routing table. Because Router C and Router B reside in different ASs, BGP does not compare the MEDs
of the two routes. Router C has a smaller router ID than Router B so the route from Router C becomes
optimal.
Network
*>i 10.0.0.0
* i 10.0.0.0
* i
However, Router C and Router A reside in the same AS, and Router C has a greater MED, so network
10.0.0.0 learned from Router C should not be optimal.
You can configure the bestroute compare-med command to enable MED comparison for routes from the
same AS on Router D. After that, Router D puts the routes received from each AS into a group, selects the
route with the lowest MED from each group, and compares routes from different groups. This mechanism
avoids the above-mentioned problem. The following output shows the BGP routing table on Router D after
this feature is enabled. Network 10.0.0.0 learned from Router B is the optimal route.
AS 400
Router ID : 1.1.1.1
Router C
Eth1/1 Eth1/1
3.3.3.3/24 1.1.1.1
AS 100
Figure 53, Router D learns network 10.0.0.0 from both Router A and Router B. Because
NextHop
2.2.2.2
3.3.3.3
NextHop
1.1.1.1
2.2.2.2
3.3.3.3
Command
ipv6-family [ unicast ]
compare-different-as-med
Router E
10.0.0.0
Router B
Router D
MED
50
50
MED
60
50
50
197
Remarks
N/A
By default, this feature is disabled.
AS 300
Router ID : 2.2.2.2
Eth1/1
2.2.2.2/24
LocPrf PrefVal Path/Ogn
0
0
LocPrf PrefVal Path/Ogn
0
0
0
300e
200e
200e
300e
200e