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).
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.
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 –
