iBGP vs eBGP –

iBGP and eBGP are both flavours of the BGP protocol. Let’s understand a short on what both terms mean before comparing the functionalities of both –

Internal BGP (Border Gateway Protocol) or iBGP –

It is the protocol used between the routers in the same autonomous system (AS).

External Border Gateway Protocol or eBGP –

It is a flavour of Border Gateway Protocol (BGP) used for communication between different autonomous systems (AS). eBGP functions as the protocol responsible for interconnection of networks from different organizations or the Internet.

eBGP is used and implemented at the edge or border router that provides interconnectivity for two or more autonomous system.

Related – BGP Local Preference Attribute

Now that we have brief of both the eBGP and iBGP protocols, below table compares them on various parameters

Difference in iBGP vs eBGP –

PARAMETER	eBGP	iBGP
Abbreviation for	External BGP	Internal BGP
Neighborship	Both the Routers forming eBGP neighborship need to be in separate AS (Autonomous Systems).	Both the Routers forming iBGP neighborship need to be in same AS (Autonomous Systems).
Route Advertisement	A route learnt from an eBGP peer will be advertised back to another IBGP or eBGP neighbor by default.	A route learnt from an IBGP peer will not be advertised back to another iBGP neighbor by default.
As Path addition	AS path is prepended to route when advertised to eBGP peer	AS path is not prepended to the route when advertised to an IBGP peer.
Attributes	Attributes like local preference are not sent to the eBGP peers but are sent to iBGP peer.	Attributes like local preference are sent to the IBGP peers but not to an EBGP peer.
Scope	Used Between organization or between organization and Internet Service provider	Used within the same organization.
TTL	By default, eBGP peers are set with TTL = 1, which means neighbors are assumed to be directly connected	By default, iBGP peers are set with TTL = 255
AD (Administrative Distance)	EBGP routes have administrative distance of 20	IBGP routes have administrative distance of 200
Next Hop attribute	Next hop is changed to local router when it is advertised to EBGP peer by default	Next hop remains unchanged when route is advertised to iBGP peer
Topology	Doesn’t require full mesh neighborship	Requires full mesh or else either of Route reflectors or Confederation
Loop prevention mechanism	Utilizes As Path for loop prevention	Uses BGP Split horizon i.e. non advertisement from iBGP to iBGP neighbor.