Objectives
The simulator ticks each one as soon as the network meets it.
eBGP: R1 (AS 65001) peers with R2 (10.0.12.2, AS 65002).
iBGP: R2 and R3 peer between loopbacks (peer connect-interface LoopBack0).
Advertise 192.168.1.0/24 on R1 and 192.168.3.0/24 on R3.
Make R2 the next hop for R3 (peer next-hop-local).
Ping PC2 from PC1.
Before you start
iBGP keeps the eBGP next hop (10.0.12.1), which R3 cannot reach because 10.0.12.0/30 is not in OSPF. show ip bgp / display bgp routing-table lists such paths without the * valid flag.
Concept
iBGP: update-source and next-hop-self
Inside one AS, routers share BGP routes over iBGP. Two details trip people up: sessions should run between loopbacks so they survive a link failure, and iBGP keeps the external next hop, which internal routers may not be able to reach.
Concept
eBGP: exchanging routes between autonomous systems
BGP connects networks run by different organisations (autonomous systems). Two routers in different ASes form an eBGP session over TCP port 179 and advertise only the prefixes they choose, each tagged with the AS path it has crossed.
