R21xx-HP FlexFabric 11900 Layer 3 IP Routing Configuration Guide

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Figure 45 NEXT_HOP attribute

• MED (Multi-Exit Discriminator)

BGP advertises the MED attribute between two neighboring ASs, each of which does not advertise

the attribute to any other AS.

Similar to metrics used by IGPs, MED is used to determine the best route for traffic going into an AS.

When a BGP router obtains multiple routes to the same destination, but with different next hops

from different EBGP peers, it considers the route with the smallest MED value the best route given

that other conditions are the same. As shown in Figure 46, traffic

from AS 10 to AS 20 travels

through Router B that is selected according to MED.

Figure 46 MED attribute

D = 9.0.0.0

Next_hop = 2.1.1.1

MED = 0

D = 9.0.0.0

Next_hop = 3.1.1.1

MED = 100

MED = 0

Router B

Router A

Router C

Router D

2.1.1.1

3.1.1.1

MED = 100

AS 20

AS 10

9.0.0.0

EBGP

IBGP