iBGP is abbreviation for Internal Border Gateway Protocol. iBGP protocol is used between the routers within the same autonomous system (AS). iBGP speaking Routers need to form full mesh to maintain full routing information. Full mesh (iBGP neighborship with all Routers in same AS) can be mitigated by using either Route reflectors or BGP confederation.
Key Features of iBGP:
iBGP Neighborship: Both the routers forming iBGP needs to be in the same Autonomous System.
iBGP Advertisement: A route learnt from an iBGP peer will not be advertised back to another iBGP neighbor by default.
iBGP Scope: iBGP is used within the same organisation.
iBGP Administrative Distance: iBGP routes have administrative distance of 200.
iBGP Toplogy: iBGP requires full mesh or else either of route reflectors or BGP confederation.
iBGP TTL: iBGP TTL is set at 255 by default
Related – iBGP