R2511-HP MSR Router Series Layer 3 - IP Routing Configuration Guide(V5)

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Step Command Remarks
2. Enter BGP view or BGP-VPN
instance view.
• Enter BGP view:
bgp as-number
• Enter BGP-VPN instance view:
a. bgp as-number
b. ipv4-family vpn-instance
vpn-instance-name
Use either method.
3. Enable the comparison of
MED of routes from different
ASs.
compare-different-as-med Not enabled by default.
Enabling the comparison of MEDs for routes on a per-AS basis
Route learning sequence might affect optimal route selection.
Figure 58 Route selection based on MED
As shown in Figure 58, 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
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 will not compare the MEDs
of the two routes. Router C 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 A reside in the same AS, and Router C has a greater MED, so network
10.0.0.0 learned from Router C is not optimal.