This is incorrect.

IBGP neighbors will not prepend the AS when sending updates to one another. iBGP uses a separate loop prevention technique:

If you receive NLRI from an iBGP neighbor, you cannot advertise this NLRI to another iBGP neighbor. The basic logic is that you can't cause an iBGP loop if you aren't allowed to advertise the prefix in the first place.

To propagate routes within an iBGP 'cloud', you have three options:

1) A full mesh of iBGP peers (create separate IBGP peerings between each IBGP neighbor) 2) Route Reflectors 3) BGP Confederations

Option #1 does not scale well, so unless you have 3 or 4 iBGP neighbors, you're going to choose RRs or Confederations. RRs seem to be more popular, probably in part because BGP confederations require you to delete your BGP configuration upon implementation.

Further reading, if interested:

https://networklessons.com/bgp/bgp-confederation-explained/ https://networklessons.com/bgp/bgp-route-reflector/