iBGP vs eBGP – Know the difference between iBGP & eBGP

iBGP & 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).

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iBGP is used to provide information to your internal routers. iBGP requires all the devices in same AS to form full mesh neighborship or either of Route reflectors and Confederation for prefix learning.

 

iBGP VS eBGP

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.

Download the difference bw iBGP vs eBGP table here.

 

 

 

 

 

Related- Dynamic BGP Peering

 

Know more about the difference in IBGP vs eBGP in this video –

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