BGP scalability: Confederation Vs Route Reflectors Hierarchical

BGP confederations:   help with the number of peering session capability

• RFC 5065
• The basic idea with confederations is to divide a normal BGP autonomous system into multiple sub-autonomous systems
  
• 1 big iBGP domain >>> SUM ( many smaller #eBGP domain )
• The outer or containing autonomous system is called the confederation autonomous system. 
  
• Reduce iBGP fully mesh network >>>> "eBGP" meshing
• But still require full mesh withing the sub-AS (#eBGP domain)

Route Reflector:   Greatly improve with the number of peering session capability

RR in a cluster:

Hierarchical RR in cluster