What is AS Confederations ?

 AS Confederations:-

 In an AS Confederation, an AS is divided into smaller Sub-autonomous systems, which are connected through EBGP to each other. Each Sub-AS acts as an independent BGP AS and runs normal IBGP internally within the Sub-AS. A single IGP is run in a complete AS and each Sub-AS has IGP routing information about all other Sub-autonomous systems. Most BGP attributes, such as LOCAL_PREF, MED, and NEXT_HOP, are preserved when updates go across a Sub-AS. The AS_PATH attribute adds the Sub-autonomous systems in the AS_PATH. To the outside world, the AS running AS Confederation appears as a single AS.

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AS Confederations, also known as Autonomous System Confederations, is a concept and technique used in Border Gateway Protocol (BGP) networks to address scalability challenges associated with large Autonomous Systems (ASes). It provides a hierarchical structure within an AS, allowing for better management of BGP routing information and reducing the complexity of full-mesh connectivity.

In BGP networks, routers within an AS typically establish full-mesh peerings, where each router maintains a direct BGP session with every other router. However, in large ASes with a significant number of routers, this full-mesh connectivity becomes difficult to manage and scale due to the increasing number of BGP peering relationships and the associated administrative overhead.

AS Confederations address this issue by dividing a large AS into smaller sub-ASes called confederations. Each confederation operates as an independent autonomous system, with its own internal BGP peering relationships. However, confederations also establish a separate set of BGP peerings with routers in other confederations to exchange routing information.

Key aspects of AS Confederations include:

Confederation Identifier (AS-ID): Each confederation is assigned a unique Confederation Identifier (AS-ID), similar to the Autonomous System Number (ASN) used in traditional BGP. The AS-ID distinguishes the confederations from one another.

Internal and External BGP (iBGP and eBGP): Within a confederation, routers establish internal BGP (iBGP) peerings to exchange routing information. iBGP ensures that routes learned within a confederation are propagated throughout that confederation.

Inter-Confederation BGP (Inter-Confed BGP): Confederations also establish external BGP (eBGP) peerings with routers in other confederations using Inter-Confederation BGP. These eBGP peerings allow the exchange of routing information between confederations.

Confederation Sub-ASes: Each confederation is further divided into sub-ASes, also known as confederation sub-ASes. The sub-ASes function similarly to traditional ASes and have their own routing policies, route selection mechanisms, and configuration.

Benefits of using AS Confederations include:

Scalability: AS Confederations improve the scalability of large ASes by reducing the number of required BGP connections and simplifying the management of routing information. The hierarchical structure of confederations allows for better control and distribution of routing information.

Reduced Resource Utilization: By establishing confederations, the number of required BGP peering relationships is significantly reduced compared to a full-mesh topology. This reduction in peering relationships reduces the resource utilization, processing overhead, and memory requirements of individual routers.

Simplified Configuration and Policy Control: AS Confederations simplify the configuration and policy control within each confederation. Routing policies can be applied at the confederation level, allowing for better management and control of routing decisions.

It's important to note that AS Confederations are primarily used in larger BGP networks where traditional mechanisms, such as route reflectors, may not be sufficient to address scalability challenges. The use of AS Confederations requires careful planning and configuration to ensure proper routing and connectivity within the overall network.