An enterprise edge router receives advertisements for the destination prefix from three distinct routing sources: an eBGP session (Administrative Distance ), an OSPF area (Administrative Distance ), and a floating static route configured with an Administrative Distance of . Currently, the router installs the eBGP route into its routing table. The network operations team requires all traffic bound for to prefer the internal OSPF path under normal operating conditions, while maintaining the eBGP path as an automatic secondary backup if OSPF fails. Which configuration change directly achieves this objective without modifying network subnets or prefixes?
- AIncrease the OSPF Administrative Distance for the prefix to a value greater than 130.
- BLower the OSPF cost metric for the route to 0.
- Increase the eBGP Administrative Distance for the route above 110 but below 130.Answer
- DChange the transport layer port number used by OSPF to match BGP port 179.
Answer
Increase the eBGP Administrative Distance for the route to a value greater than OSPF (110) but less than the floating static route (130).
When a router learns the exact same destination prefix through multiple routing sources, it evaluates Administrative Distance (AD) first. Lower AD values indicate higher trust. By increasing the eBGP AD for the route to a value between 111 and 129, OSPF (AD 110) becomes the primary active route in the routing table, while eBGP (e.g., AD 120) remains available as the secondary backup before the floating static route (AD 130).
Step-by-Step Solution
Key Concept
Administrative Distance Hierarchy and Multi-Protocol Path Selection