How to Use Policy in Juniper Networks to Ensure Route Usability
Question
-- Exhibit --
[edit]
user@Router-X# show policy-options policy-statement nhs
term 1 {
from {
protocol bgp;
neighbor 10.0.21.2;
}
then next-hop self;
}
-- Exhibit --
Click the Exhibit button.
Router-X has an external peering session to 10.0.21.2 and several internal peers.
How can the policy referenced in the exhibit be used to make sure routes are usable?
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D.B
The given policy statement named "nhs" is used to set the next-hop for BGP routes received from the neighbor IP address 10.0.21.2 to the local router's own IP address (self).
To ensure that routes are usable, the policy statement can be applied as either an import or export policy to BGP peers, depending on the direction of routing updates.
Import policy: When applied as an import policy, the policy statement is evaluated when BGP routes are received from external (i.e., eBGP) peers. This ensures that the next-hop for these routes is set to the local router's own IP address before the routes are installed in the routing table. This is necessary because by default, BGP routes received from external peers are not installed in the routing table if their next-hop is not reachable.
So, to use the policy statement to make sure routes are usable, it should be applied as an import policy to external BGP peers. Therefore, option C is the correct answer.
Export policy: When applied as an export policy, the policy statement is evaluated when BGP routes are advertised to external (i.e., eBGP) peers. This ensures that the next-hop for these routes is set to the local router's own IP address before the routes are sent to external peers. This is necessary because external peers must have a valid next-hop for the routes to be used.
Therefore, option D is an incorrect answer because applying the policy statement as an export policy to external BGP peers would not ensure the usability of routes. Similarly, applying the policy statement as an import or export policy to internal BGP peers (options A and B) would not ensure the usability of routes.
