Dual BGP Peering Solution with Cisco Service Provider
Question
An engineer is tasked with designing a dual BGP peering solution with a service provider.
The design must meet these conditions: * The routers will not learn any prefix with a subnet mask greater than /24
* The routers will determine the routes to include in the routing table based on the length of the mask alone.
* The routers will make this selection regardless of the service provider configuration.
Which solution should the engineer include in the design?
Answers
Explanations
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A. B. C. D.D.
The engineer is tasked with designing a dual Border Gateway Protocol (BGP) peering solution with a service provider. The solution must ensure that the routers do not learn any prefix with a subnet mask greater than /24 and that the routers determine the routes to include in the routing table based on the length of the mask alone. The routers should make this selection regardless of the service provider configuration.
To meet these conditions, the engineer can use an IP prefix list to block the desired networks and apply the IP prefix list to BGP neighbors inbound. Therefore, the correct solution is option D.
An IP prefix list is a sequential list of network prefixes and their subnet masks. It is used to filter traffic based on IP addresses or network prefixes. In this scenario, the IP prefix list can be used to block the desired networks by specifying the network prefixes with a subnet mask greater than /24. The IP prefix list can then be applied to BGP neighbors inbound to prevent the routers from learning these prefixes.
Applying the IP prefix list inbound means that the filtering is done before the prefixes are added to the BGP table. This ensures that the prefixes are not learned, and as a result, they will not be included in the routing table.
Using a route map and access list to block the desired networks, and applying the route map to BGP neighbors inbound (Option A) can also work. However, using an IP prefix list is a more efficient and recommended solution in this scenario.
Using a route map and prefix list to block the desired networks, and applying the route map to BGP neighbors outbound (Option B) can also work, but it would not meet the requirement that the routers determine the routes to include in the routing table based on the length of the mask alone.
Using an IP prefix list to block the desired networks and apply the IP prefix list to BGP neighbors outbound (Option C) would not meet the requirement that the routers determine the routes to include in the routing table based on the length of the mask alone.
In summary, Option D is the correct solution.
