BGP Mechanisms

CE.

The BGP (Border Gateway Protocol) full-mesh paradigm refers to the requirement of establishing a full mesh of iBGP (internal BGP) peering sessions between all routers within an AS (Autonomous System). However, this approach does not scale well as the number of routers in the AS grows. To overcome this issue, the following two mechanisms were introduced to solve the BGP full-mesh paradigm:

1. Route Reflectors: A route reflector (RR) is a BGP router that can act as a central point of reflection for BGP routing updates. In this approach, a subset of iBGP routers called clients are configured to peer with the RR. The RR then propagates the BGP updates it receives from its clients to all other iBGP routers in the AS. This approach reduces the number of iBGP sessions required for full-mesh connectivity, thus simplifying the BGP configuration and reducing the memory and CPU requirements on the routers.

2. Confederation: A confederation is a technique used to break up an AS into smaller sub-ASes that can be managed independently. In this approach, routers within the same sub-AS peer with each other using iBGP, while routers in different sub-ASes peer using eBGP (external BGP). The confederation is identified by a unique AS number that is shared by all the routers in that sub-AS. This approach can be used to scale a large AS into smaller, more manageable parts.

Therefore, the correct answers are C. Route Reflectors and E. Confederation. The other options mentioned in the question, BGP link state, MPLS VPN, hierarchical VPLS, route policy filtering, and community SOO are not relevant to solving the BGP full-mesh paradigm.