An enterprise border router maintains two paths to reach a remote corporate subnet (). Path 1 is learned via internal BGP (iBGP) with an Administrative Distance (AD) of 200, while Path 2 is learned via Open Shortest Path First (OSPF) with an AD of 110. Both routes report the exact same prefix length (). Network monitoring shows that traffic is actively taking Path 2 over the low-bandwidth OSPF backup link instead of the primary iBGP connection. Which configuration modification should the network administrator perform on the border router to ensure traffic prefers the primary iBGP link under normal operations?
- Decrease the Administrative Distance for the learned iBGP route to a value lower than 110.Cevap
- BIncrease the OSPF cost metric on the backup interface to a value higher than the BGP MED attribute.
- CConfigure static Port Address Translation (PAT) on the OSPF interface to force traffic to egress through the iBGP interface.
- DReconfigure the default gateway on local hosts to point to the remote host address residing in the subnet.
Cevap
Decreasing the Administrative Distance of the iBGP route below 110 ensures the router prefers the primary iBGP link.
When a router receives multiple routes to the same network prefix with identical prefix lengths, it chooses the route with the lowest Administrative Distance (AD). Standard iBGP has a default AD of 200, whereas OSPF has a default AD of 110. Because 110 is lower than 200, the router prefers the OSPF path. Lowering the AD for the iBGP route below 110 ensures the router selects the iBGP path as primary while maintaining OSPF as the secondary backup path.
Adım Adım Çözüm
Anahtar Kavram
Route Selection Hierarchy and Administrative Distance Preference