Analyzing the Exhibit
* The diagram represents BGP peering between:
* AS 65512 (Enterprise Network)
* AS 65511 (ISP-A)
* R3 and R4 are peering with ISP-A using EBGP.
* R1, R2, R3, and R4 are peering within AS 65512 using IBGP.
Understanding BGP Route Behavior
Option A: "By default, the next-hop value for these routes is not changed by ISP-A before being sent to R3." #
* Incorrect!
* EBGP behavior: When a BGP route is advertised via EBGP, the next-hop IP is changed to the router's own IP by default.
* Since ISP-A is advertising routes via EBGP to R3, the next-hop is changed to ISP-A's IP.
* Thus, this statement is incorrect.
Option B: "The BGP local-preference value that is used by ISP-A is not advertised to R3." #
* Correct!
* BGP Local Preference (LOCAL_PREF) is an IBGP-only attribute.
* Local Preference is NOT shared over EBGP because it is used within an AS to influence route selection.
* ISP-A will not send LOCAL_PREF to R3, as R3 is in a different AS.
* Thus, this statement is correct.
Option C: "All BGP attribute values must be removed before receiving the routes." #
* Incorrect!
* BGP does not remove all attributes when advertising routes. Some attributes are modified (e.g., next- hop, AS-PATH), but others (like MED, community) may be preserved.
* Thus, this statement is incorrect.
Option D: "The next-hop value for these routes is changed by ISP-A before being sent to R3." #
* Correct!
* As per default EBGP behavior, the next-hop is changed when a route is advertised to an EBGP peer.
* This means ISP-A changes the next-hop to its own IP before sending it to R3.
* Thus, this statement is correct.
# B. The BGP local-preference value that is used by ISP-A is not advertised to R3.
# D. The next-hop value for these routes is changed by ISP-A before being sent to R3.
Verification from Juniper Documentation:
* Juniper BGP Configuration Guide confirms that LOCAL_PREF is not advertised over EBGP.
* RFC 4271 (BGP-4) specifies that next-hop is changed by default when advertising routes via EBGP
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