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Click the Exhibit button. You are troubleshooting an issue for a customer site that uses 10.10.0.0/24 in AS 65224, but you see another AS in the AS path. Referring to the exhibit, what is the cause of the problem?
Correct Answer: A
In the given exhibit, you are observing the BGP routing information for the prefix 10.10.0.0/24. The AS path for this prefix shows `65000 {65137 65224}`. To understand the issue, let's analyze each aspect of the information provided and the options given: 1. **AS Path Analysis**: - The AS path attribute in BGP is a list of AS numbers that a route advertisement has traversed. - In this case, the AS path `65000 {65137 65224}` indicates that the route to 10.10.0.0/24 has been advertised through AS 65000, which includes AS 65137 and AS 65224. 2. **Understanding AS Path Prepending**: - AS path prepending is a technique used by AS administrators to artificially lengthen the AS path. - By adding their own AS number multiple times into the AS path, they make a route less attractive to others. - Here, AS 65000 is showing `65137` as part of its AS path, suggesting it might be prepending to manipulate routing decisions. 3. **Options Analysis**: - **Option A**: "AS 65000 is pre-pending AS 65137 to route advertisements." - This option suggests that AS 65000 is deliberately adding AS 65137 to the AS path. This matches the observed AS path, where AS 65000 has prepended `65137`. - Therefore, this is the correct explanation. - **Option B**: "The local AS is receiving two equal cost routes to 10.10.0.0/24." - There is no evidence in the exhibit to support the presence of two equal-cost routes. - **Option C**: "The local AS is in the process of withdrawing the route from AS 65137." - Route withdrawal would not cause the AS path to include `65000 {65137 65224}`. - **Option D**: "AS 65137 is advertising the 10.10.0.0/24 prefix." - While AS 65137 is part of the path, it does not explain the presence of AS 65000 in the path, making this option incorrect. **Conclusion**: The AS path `65000 {65137 65224}` is indicative of AS 65000 prepending AS 65137. Therefore, the correct answer is: **A. AS 65000 is pre-pending AS 65137 to route advertisements.** **References**: - Juniper Networks documentation on BGP AS path manipulation and prepending techniques. - BGP Best Practices and Routing Policies: [Juniper Networks BGP Best Practices](https://www.juniper.net/documentation/en_US/junos/topics/concept/bgp-best-practices-routing-policie - RFC 4271, A Border Gateway Protocol 4 (BGP-4): [RFC 4271](https://tools.ietf.org/html/rfc4271) which describes the behavior and attributes of BGP, including AS path prepending.