iBGP vs eBGP: Understanding the Differences
In the intricate world of routing protocols, the Border Gateway Protocol (BGP) stands as a pillar, facilitating the exchange of routing information between different networks on the internet. Within BGP, two fundamental variations exist: Internal BGP (iBGP) and External BGP (eBGP). Both serve distinct purposes in managing routing within and between Autonomous Systems (ASes).
Internal BGP (iBGP)
Definition: iBGP operates within a single Autonomous System, allowing communication and sharing of routing information between routers belonging to the same AS.
- Within AS Communication: iBGP is employed for routers within an AS to exchange routing information. It ensures that all routers within the AS have consistent and updated routing tables.
- Full Mesh or Route Reflector: In iBGP, all routers traditionally form a full mesh, directly peering with each other. Alternatively, a route reflector configuration can be used, where some routers serve as route reflectors to reduce the need for full-mesh connections.
- Preservation of Next-Hop Information: iBGP maintains the original next-hop information, ensuring the path selection remains accurate within the AS.
External BGP (eBGP)
Definition: eBGP operates between different Autonomous Systems, allowing communication and exchange of routing information between routers belonging to different ASes.
- Inter-AS Communication: eBGP enables the exchange of routing information between different ASes, facilitating the propagation of routes across the internet.
- Neighbor Relationships: eBGP establishes neighbor relationships between routers in different ASes. Peering between these routers occurs over external connections.
- Path Attributes Manipulation: eBGP modifies path attributes like AS Path, allowing routers to make intelligent routing decisions and prevent loops in inter-domain routing.
Key Differences and Use Cases
Scope of Operation:
- iBGP: Operates within a single AS, facilitating internal routing and maintaining consistent routing tables.
- eBGP: Operates between different ASes, facilitating the exchange of routing information between networks.
- iBGP: Does not alter the next-hop information and focuses on distributing internal routes within the AS.
- eBGP: Modifies path attributes and disseminates routing information between different ASes across the internet.
- iBGP: Usually utilizes a full mesh or route reflector topology within an AS.
- eBGP: Establishes peer connections between routers in different ASes over external links.