— Exhibit –
— Exhibit —
Click the Exhibit button.
Referring to the exhibit, your AS is connected to ISP-A and ISP-B using BGP. R1 and R2 are
advertising your AS’s 172.25/16 prefix upstream to both ISPs, and both ISPs are providing a full
BGP route table. You want to influence traffic flow so that traffic towards your network enters
through R1.
Which action would meet the requirement?
Apply the following as an export policy towards ISP-B:
A.
[edit policy-options]
user@R2# show
policy-statement prefer-for-inbound {
term prepend {
then {
as-path-prepend “100 100”;
accept;
}
Apply the following as an export policy towards ISP-A:
B.
[edit policy-options]
user@R1# show
policy-statement prefer-for-inbound {
term prepend {
then {
as-path-prepend “100 100”;
accept;
}
Apply the following as an export policy towards R1 and R3:
C.
[edit policy-options]
user@R2# show
policy-statement prefer-for-inbound {
term local-pref {
then {
local-preference 110;
accept;
}
Apply the following as an export policy towards R2 and R3:
D.
[edit policy-options]
user@R1# show
policy-statement prefer-for-inbound {
term local-pref {
then {
local-preference 110;
accept;
}
Who can explain me this, why answer a ?
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You want influence traffic to use R1 when ENTERING your network.
Therefore, you need to make path through R2 ‘worse’.
For that, you can prepend your AS number few times to as-path in all prefixes advertised by R2, and thanks to that, prefixes from R2 are worse than R1 (longer AS Path).
And since AS path is a transitive mandatory attribute, it will be propagated thorough ASes.
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This is not right….A will be correct if it is applied to the eBGP facing ISP B not ISP A.. R2 is connected to ISP B not A….so there is no correct answer,….
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I believe this is a typo “Apply the following as an export policy towards ISP-A”….so if it is ISP-B, then A is the correct answer
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Should be:
A.
Apply the following as an export policy towards ISP-B:
[edit policy-options]
user@R2# show
policy-statement prefer-for-inbound {
term prepend {
then {
as-path-prepend “100 100”;
accept;
}
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0