IBGP

What is IBGP?

Internal Border Gateway Protocol (IBGP) is a protocol used within a single Autonomous System (AS) to exchange routing information between routers. Unlike Exterior Border Gateway Protocol (EBGP), which is used to exchange routing information between different ASes, IBGP operates within the same AS. It is designed to ensure that all routers within the AS have consistent routing information, enabling efficient forwarding of traffic within the network.

IBGP establishes peering relationships between routers within the same AS, forming a full mesh or partial mesh topology. Routers in an AS use IBGP to propagate routing information learned from external sources (e.g., EBGP peers) throughout the internal network. This ensures that all routers have consistent and up-to-date routing tables, allowing them to make informed decisions about the best paths to reach different destinations within the AS.

IBGP Use Cases.

Internal Border Gateway Protocol (iBGP) is a crucial component of modern network architectures, facilitating efficient routing within an Autonomous System (AS). Let's delve into the key aspects and benefits of iBGP:

Internal Routing within AS: iBGP operates within a single AS, allowing routers to exchange routing information without the need for external routing protocols.

Full Mesh Topology: iBGP typically employs a full mesh topology, where each router establishes a direct BGP session with every other router within the AS. This ensures comprehensive route distribution and convergence.

Scalability and Flexibility: By supporting full mesh connectivity, iBGP enables scalable and flexible network designs. It accommodates diverse network topologies and growth scenarios, making it suitable for both small-scale enterprises and large ISPs.

Traffic Engineering: iBGP offers granular control over traffic engineering within an AS. Network administrators can influence route selection based on factors such as link bandwidth, latency, and policy requirements, optimizing network performance.

Redundancy and High Availability: By establishing redundant paths and failover mechanisms, iBGP enhances network redundancy and high availability. It ensures continuous connectivity even in the event of link failures or network disruptions

In summary, iBGP plays a pivotal role in enabling efficient routing, scalability, and resilience within Autonomous Systems. Its full mesh topology, scalability, traffic engineering capabilities, and contributions to redundancy make it a fundamental protocol in modern networking.

iBGP Intricacies

• Split-horizon: In iBGP, by default, a router will not advertise a route learned from one iBGP peer to another iBGP peer. This is because iBGP does not modify the AS path attribute, and if a router advertises a route with its own AS number in the AS path, it could cause a routing loop. To overcome this limitation, use route reflectors or configure the next-hop-self command.
• AS-Path: In iBGP, the AS path attribute is not modified. Therefore, iBGP does not provide any loop prevention mechanism. If a router receives a route with its own AS number in the AS path attribute, it will not install the route in its routing table. This means that you need to ensure that your network design does not allow for loops to occur
• Synchronization: In iBGP, the synchronization rule states that a router should not advertise a route learned from an iBGP peer to an eBGP peer unless the router has learned the same route from an IGP (Interior Gateway Protocol) or another eBGP peer. This rule ensures that all routers in the AS have the same view of the network. However, this rule can cause suboptimal routing if the IGP does not converge quickly enough.
• Path Attributes: In iBGP, all path attributes are propagated unchanged from one iBGP peer to another iBGP peer. This means that any path attributes set by an eBGP peer will be propagated to other iBGP peers. To address this, you can use the remove-private-as command.