Comprehensive and Detailed in-depth Step-by-Step Explanation:BGP confederations are used to reduce the complexity of IBGP full-mesh connections within a large AS by dividing the AS into multiple sub-ASs (called "member ASs") while still appearing as a single AS to external ASs. Below is an analysis of each option:
* A. The ASs outside a confederation still consider the confederation as one AS:
* This is true. Externally, the entire confederation is seen as a single AS, identified by the main AS number.
* B. After a confederation is configured, the original IBGP attributes can be retained:
* This is true. The configuration of a confederation does not affect the IBGP attributes exchanged between routers.
* C. After a confederation is configured, the original AS number is used as the confederation ID of each router:
* This is true. The main AS number is used as the Confederation Identifier for all member ASs in the confederation.
* D. A confederation divides an AS into several sub-ASs, and EBGP full-mesh connections are established in each sub-AS:
* This is false. Within each sub-AS of a confederation, IBGP connections are still used (not EBGP). Confederations are designed to reduce the number of IBGP full-mesh connections required within a large AS by creating smaller, manageable sub-ASs.
Therefore, the correct answer is D.
References:
* Huawei HCIA-Datacom Study Guide, Chapter on "BGP Confederations".
* RFC 5065 - Autonomous System Confederations for BGP.