CompTIA Network+ (N10-009)Network ImplementationMedium
A router has two routes to the same destination network: one learned via eBGP from an external autonomous system and one learned via iBGP from a router within the same AS. Both routes have default administrative distances and no other tie-breaking policy has been configured. Which route will the router prefer?
- ABoth routes will be installed and load-balanced equally
- BThe eBGP route, because it has a lower administrative distance
- CThe iBGP route, because it is internal and more trusted
- DNeither route will be installed until OSPF confirms it
Show answer & explanationAnswer & explanation
Correct answer: B. The eBGP route, because it has a lower administrative distance
eBGP routes have a default administrative distance of 20, while iBGP routes have a default administrative distance of 200; since lower AD is preferred, the router installs the eBGP-learned route in this scenario.
Why the other options are wrong
- A. BGP does not equal-cost load-balance across eBGP/iBGP by default without specific configuration.
- C. iBGP has a higher (less preferred) default AD of 200 compared to eBGP's 20.
- D. OSPF is unrelated to BGP's internal route selection process.
eBGP vs iBGP Administrative Distance
BGP routes learned from external peers (eBGP) have a default AD of 20, while routes learned from internal peers (iBGP) have a default AD of 200, making eBGP routes preferred by default.
- eBGP default AD = 20
- iBGP default AD = 200
- Lower AD wins when comparing routes to the same destination
Memory trick: 'e' comes before 'i' in the alphabet, and eBGP's AD (20) beats iBGP's (200).