— Exhibit —
— Exhibit —
Click the Exhibit button.
Referring to the exhibit, you must ensure that traffic to the 2001:10:5::/64 network leaves AS 2
through R3.
Given that all BGP attributes are at their default, how would you accomplish this task?
A.
On R1, configure a MED of 50 for the 2001:10:5::/64 route.
B.
On R2, configure a MED of 50 for the 2001:10:5::/64 route.
C.
On R3, configure a MED of 50 for the 2001:10:5::/64 route.
D.
On R4, configure a MED of 50 for the 2001:10:5::/64 route.
How can the answer be B?
Because BGP prefer the lowest MED value, so you want to apply on the router where you need to have that traffic.
I think is A
Default MED value is 100, so you configure a lower value (50) in the preferred entry point (in this case, R1, because is the peer with R3, the preferred exit point)
Answer-B
If the received route does not have an associated MED metric, and if you do not explicitly configure a metric value, no metric is advertised. When you do not explicitly configure a metric value, the MED value is equivalent to zero (0) when advertising an active route.
B is the correct answer.
On Junos, by default the absent of a MED value is interpreted as MED 0, the lowest the MED the better.
Route 2001:10:5::/34 learned on AS2 twice from two different Routers on the same AS, Routers on AS2 compared the BGP attributes in order to determine which route will be the active route and everything is the same until they check the MED vaule, they see a MED value of 0 for R1 (this because MED was not configured on R1) and a MED value of 50 for R2. The lowest the better, R1 is the winner.
Understanding BGP path selection
http://www.juniper.net/techpubs/en_US/junos12.3/topics/reference/general/routing-ptotocols-address-representation.html
-“Meditation is the medicine of the mind”