352-011 · Question #51
A data center provider has designed a network using these requirements Two data center sites are connected to the public internet Both data centers are connected to different Internet providers…
This question has formatting issues - choices A, B, C, and E appear to be truncated/identical, and the correct answer field is blank. However, this is a classic BGP subnet design question (common in CCNP-level exams), so I can explain the underlying concept and the two correct…
Question
A data center provider has designed a network using these requirements Two data center sites are connected to the public internet Both data centers are connected to different Internet providers Both data centers are also directly connected with a private connection for the internal traffic can also be at this direct connection The data center provider has only /19 public IP address block Under normal conditions, Internet traffic should be routed directly to the data center where the services are located. When one Internet connections fails to complete traffic for both data centers should be routed by using the remaining Internet connection in which two ways can this routing be achieved? (Choose two)
Options
- AOne /20 block is used for the first data center and the second /20 block is used for the second data
- BOne /20 block is used for the first data center and the second /20 block is used for the second data
- COne /20 block is used for the first data center and the second /20 block is used for the second data
- DBGP will always load-balance the traffic to both data center sites
- EOne /20 block is used for the first data center and the second /20 block is used for the second data
- FThe data center provider must have an additional public IP address block for this routing
Explanation
This question has formatting issues - choices A, B, C, and E appear to be truncated/identical, and the correct answer field is blank. However, this is a classic BGP subnet design question (common in CCNP-level exams), so I can explain the underlying concept and the two correct approaches.
The two correct answers are typically:
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Split the /19 into two /20 blocks - assign one /20 to each data center. Each DC advertises its own /20 to its local ISP. Because BGP prefers more-specific routes, internet traffic naturally flows directly to whichever DC owns that subnet (normal operation).
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Each DC also advertises the full /19 aggregate - as a less-specific backup route. When one ISP link fails, the surviving DC's ISP sees the /19 advertisement and routes all traffic (both /20s) through that remaining connection, since no more-specific /20 route exists from the failed site.
Why D is wrong: BGP does not "always load-balance." It selects a single best path per prefix using attributes (AS path length, local preference, MED, etc.). Equal-cost load balancing requires explicit configuration and isn't the default behavior.
Why F is wrong: No additional IP space is needed. A /19 natively splits into exactly two /20 blocks, which is sufficient for this design.
Memory tip: Think "specific for normal, aggregate for failover." More-specific routes win in BGP, so use /20s to direct traffic normally - but keep the /19 advertised everywhere as your emergency exit ramp.
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