A routing protocol implements route import, routing information can be transferred between different routing protocols. Which of the following problems may also be caused? (Multiple choice)

Question

Options

• ARouting black hole
• BIncorrect number conflict
• CRouting loop
• DSuboptimal path

• A
  82% (46)
• C
  5% (3)
• D
  13% (7)

Explanation

Route import (redistribution) forces routing information across protocol boundaries that were never designed to share a common metric or path-awareness model. A (routing black hole) occurs when a router advertises imported routes as reachable but lacks a complete forwarding path to the destination - traffic enters and disappears. B (incorrect number/metric conflict) occurs because protocols like RIP, OSPF, and BGP use incompatible metric systems; when routes are imported, the seed metric may conflict with or override legitimate route entries, causing inconsistent routing tables. C (routing loop) is a risk of mutual redistribution (Protocol A ↔ Protocol B simultaneously), not of route import itself - a one-directional import does not inherently create a loop, so it is not a direct consequence of the import mechanism. D (suboptimal path) is similarly a metric-tuning or design issue that can appear in any protocol, not a problem uniquely introduced by route import.

Memory tip: Route import causes "Black holes and Bad numbers" - both start with B, and both stem from the same root cause: protocols speaking different "languages" when routes cross boundaries.

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