Editing Border Gateway Protocol (section)

===Confederation===
Confederations are sets of autonomous systems. In common practice,<ref>{{cite web|url=http://www.ietf.org/rfc/rfc5065.txt |title=Info |publisher=www.ietf.org |access-date=2019-12-17}}</ref> only one of the confederation AS numbers is seen by the Internet as a whole. Confederations are used in very large networks where a large AS can be configured to encompass smaller more manageable internal ASs.

The confederated AS is composed of multiple ASs. Each confederated AS alone has iBGP fully meshed and has connections to other ASs inside the confederation. Even though these ASs have eBGP peers to ASs within the confederation, the ASs exchange routing as if they used iBGP. In this way, the confederation preserves next hop, metric, and local preference information. To the outside world, the confederation appears to be a single AS. With this solution, iBGP transit AS problems can be resolved as iBGP requires a full mesh between all BGP routers: large number of TCP sessions and unnecessary duplication of routing traffic.{{clarify|reason=My guess is this is trying to say that using eBGP within a confederation avoids scaling issues that would exist if iBGP were used instead.|date=October 2022}}

Confederations can be used in conjunction with route reflectors. Both confederations and route reflectors can be subject to persistent oscillation unless specific design rules, affecting both BGP and the interior routing protocol, are followed.<ref>{{cite web|url=http://www.ietf.org/rfc/rfc3345.txt |title=Info |publisher=www.ietf.org |access-date=2019-12-17}}</ref>

These alternatives can introduce problems of their own, including the following:
* route oscillation
* sub-optimal routing
* increase of BGP convergence time<ref>{{cite web|url=http://www.ietf.org/rfc/rfc4098.txt |title=Info |publisher=www.ietf.org |access-date=2019-12-17}}</ref>

Additionally, route reflectors and BGP confederations were not designed to ease BGP router configuration. Nevertheless, these are common tools for experienced BGP network architects. These tools may be combined, for example, as a hierarchy of route reflectors.