Which statement correctly differentiates iBGP from eBGP?

Which statement correctly differentiates iBGP from eBGP?

• A. iBGP uses TTL=2; eBGP uses TTL=1
• B. eBGP uses TTL=1; iBGP uses full mesh or route reflectors
• C. iBGP requires multi-hop; eBGP requires direct connection only
• D. eBGP does not propagate routes learned from iBGP to other iBGP peers

Answer: (B)

The important idea here is how BGP sessions and route propagation differ inside an AS versus between ASes. For eBGP, peers are in different autonomous systems and are typically directly connected, so the session uses a TTL of 1 to ensure the neighbor is truly adjacent. Inside the same AS, iBGP sessions can span multiple hops, so there isn’t a strict TTL=1 requirement; instead, all iBGP peers must be connected in a way that ensures the routes are visible to every speaker. Since iBGP does not re-advertise routes learned from one iBGP neighbor to another iBGP neighbor, you need either a full mesh of iBGP peers or route reflectors to distribute those routes throughout the AS. That’s why the correct statement is that eBGP uses TTL=1, while iBGP relies on a full mesh or route reflectors to share routes. The other options mix up TTL usage or misstate how routes learned via iBGP propagate to other peers, which doesn’t fit how BGP actually handles these session types.

The important idea here is how BGP sessions and route propagation differ inside an AS versus between ASes. For eBGP, peers are in different autonomous systems and are typically directly connected, so the session uses a TTL of 1 to ensure the neighbor is truly adjacent. Inside the same AS, iBGP sessions can span multiple hops, so there isn’t a strict TTL=1 requirement; instead, all iBGP peers must be connected in a way that ensures the routes are visible to every speaker. Since iBGP does not re-advertise routes learned from one iBGP neighbor to another iBGP neighbor, you need either a full mesh of iBGP peers or route reflectors to distribute those routes throughout the AS.

That’s why the correct statement is that eBGP uses TTL=1, while iBGP relies on a full mesh or route reflectors to share routes. The other options mix up TTL usage or misstate how routes learned via iBGP propagate to other peers, which doesn’t fit how BGP actually handles these session types.