How BGP advertises

Split horizon is always enabled, NO MATTER WHAT.

• eBGP ==> eBGP: Next-hop for the destination will be set to: The interface doing the advertisement unless use: update-source
• eBGP ==> iBGP: Next-hop for the destination will be set to: The interface of the eBGP doing the advertisement unless use: update-source, the iBGP peer must have a route [via IGP] to next-hop subnet, or won't go into BGP routing table Have the iBGP router do the next-hop-self If next-one does not have ebgp interface in routing table ==> next-hop-self
• iBGP ==> eBGP: Next-hop for the destination will be set to: The interface doing the advertisement unless you use: update-source
• iBGP ==> iBGP: Next-hop for the destination will be set to: iBGP peers do not advertise routes to other iBGP peers