Click the Exhibit button.
Both the R1 and R2 devices are advertising prefix X into AS 65530 with the BGP attributes shown in the exhibit.
Which statement is correct in this scenario?
A. R2’s version of prefix X will be active because of the local preference attribute.
B. R1’s version of prefix X will be active because of the local preference attribute.
C. R1’s version of prefix X will be active because of the AS path attribute.
D. R2’s version of prefix X will be active because of the AS path attribute.
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How is the answer B, is an internal AS option to select the best route/path out of an AS.
It has to be D if you know how BGP works.
No, you are wrong.
You can use the local-preference attribute to direct all outbound traffic through a specific peer. Before sending the traffic to the internal peers, the designated peer sets the local-preference value on all routes received. Then all the peers use those routes in their RIB-local tables. The local-preference attribute is a numeric value; higher values indicate a better metric. BGP uses the local-preference attribute only within an AS. Local-preference values are not transmitted across EBGP links. In other words: R1 sends Prefix X (which is outside the AS) with a higher local preference than R2. R3 will receive the prefix from both R1 and R2 and when it has traffic to transmit to this prefix (which means the traffic travels from R3 -> R1/R2 -> other AS, inside to outside) it will look at local preference first. AS-Path is used to manipulate traffic from outside to inside.
The answer must be D.
Reason: R1’s AS path list contains 65530，so it is never advertised into 65530, so only R2 to be selected due to as-path attribute.
I think its wrong in question.. it should be 65503..If 65530 then D otherwise B
Local Preference fist before AS path. The answer is B
Stop being silly and read up on how BGP works. Local Pref is an attribute for the best path LEAVING your network. AS Path is an attribute for routs ENTERING your network?
Look at the diagram. All 3 routers are in AS 65503, so this is IBGP. Look at the red arrows, R1 and R2 are pointing towards R3 which indicates the direction of traffic/packets. So these routes received from an EBGP peer towards an IBGP peer. If this is the case then AS Path is the answer.
If the red arrows were from R3 towards R1 and R2, then Local Pref would be the answer
On a side note, where R1 is showing AS 65530, I think this is a TYPO and should be 65503 as this would be a prepend configuration to make R2 the prefered route into the network.
You can use the local-preference attribute to direct all outbound traffic through a specific peer. Before sending the traffic to the internal peers, the designated peer sets the local-preference value on all routes received. Then all the peers use those routes in their RIB-local tables. The local-preference attribute is a numeric value; higher values indicate a better metric. BGP uses the local-preference attribute only within an AS. Local-preference values are not transmitted across EBGP links. In other words: R1 sends Prefix X (which is outside the AS) with a higher local preference than R2. R3 will receive the prefix from both R1 and R2 and when it has traffic to transmit to this prefix (which means the traffic travels from R3 -> R1/R2 -> other AS, inside to outside) it will look at local preference first. AS-Path is used to manipulate traffic from outside to inside.
local preference is first compare to AS path for BGP path selection sequence . So answer is B
LEARN HOW BGB WORKD BEFORE LEAVING AN OPINION.
Local Pref is an attribute for the best path LEAVING your network. AS Path is an attribute for routs ENTERING your network?
Look at the diagram. All 3 routers are in AS 65503, so this is IBGP. Look at the red arrows, R1 and R2 are pointing towards R3 which indicates the direction of traffic/packets. So these routes received from an EBGP peer towards an IBGP peer. If this is the case then AS Path is the answer.
If the red arrows were from R3 towards R1 and R2, then Local Pref would be the answer
On a side note, where R1 is showing AS 65530, I think this is a TYPO and should be 65503 as this would be a prepend configuration to make R2 the preferred route into the network.
Arrows are pointing at the BGP advertisement direction, traffic is opposite to the advertisement, so traffic is leaving