You are developing the routing design for two merging companies that have overlapping IP address space. What must you consider when developing the routing and NAT design?

Question

Options

• AGlobal to local NAT translation is done before routing.
• BLocal to global NAT translation is done after routing.
• CGlobal to local NAT translation is done after policy-based routing.
• DLocal to global NAT translation is done before policy-based routing.

• A
  78% (14)
• B
  6% (1)
• C
  6% (1)
• D
  11% (2)

Explanation

Understanding NAT operation order is critical when overlapping address space exists. On Cisco IOS, the order of operations differs by traffic direction: for inbound packets (outside-to-inside), 'global-to-local' translation (destination NAT) occurs BEFORE the routing lookup. This means the router first translates the packet's destination address from the outside global IP to the inside local IP, then makes its routing decision based on the translated address. For outbound packets (inside-to-outside), 'local-to-global' translation (source NAT) occurs AFTER the routing lookup. This ordering is essential when designing NAT for overlapping address spaces because the routing table must contain routes for the post-translation (local) addresses, not the pre-translation (global) addresses, for inbound flows. Misunderstanding this ordering leads to incorrect route table design and broken connectivity.

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