H3C Technologies H3C SR8800 - Manual (Page 237)

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When Router D learns network 10.0.0.0 from Router C which has a smaller router ID than Router B, the
route from Router C becomes optimal.
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.0.0.0 1.1.1.1 60 0 200e
* i 10.0.0.0 2.2.2.2 50 0 300e
* i 3.3.3.3 50 0 200e
However, Router C and Router B reside in the same AS, and BGP will compare the MEDs of them. Since
Router C has a greater MED, network 10.0.0.0 learned from it is not optimal.
You can configure the bestroute compare-med command on Router D. After that, Router D will put routes
received from the same AS into a group. For the same group, the route with the lowest MED is selected.
Then, it compares routes from different groups. This mechanism avoids the above-mentioned problem.
The following output is the BGP routing table on Router D after the comparison of MED of routes from
each AS is enabled. Network 10.0.0.0 learned from Router C is the optimal route.
Network NextHop MED LocPrf PrefVal Path/Ogn
*>i 10.0.0.0 3.3.3.3 50 0 200e
* i 10.0.0.0 2.2.2.2 50 0 300e
* i 1.1.1.1 60 0 200e
BGP load balancing cannot be implemented because load balanced routes must have the same AS-path
attribute.
To enable the comparison of MED of routes from each AS:
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 each AS.
bestroute compare-med
Optional
Not enabled by default
Enabling the comparison of MED of routes from confederation peers
To enable the comparison of MED of routes from confederation peers:
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 confederation peers.
bestroute med-confederation
Optional
Not enabled by default
NOTE:
The MED attributes of routes from confederation peers are not compared if their AS-path attributes contain
AS numbers that do not belong to the confederation, such as these three routes: AS-path attributes of them
are 65006 65009, 65007 65009 and 65008 65009, and MED values of them are 2, 3, and 1. Because
the third route contains an AS number that does not belong to the confederation, the first route becomes
the optimal route.