Border Gateway Protocol

Border Gateway Protocol. It is the standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems on the Internet. The protocol is classified as a path vector protocol, and it makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator. BGP plays a critical role in the global routing system, enabling the decentralized network of networks that constitutes the modern Internet.

Overview

The protocol was first defined in 1989 in RFC 1105, authored by Kirk Lougheed and Yakov Rekhter of Cisco Systems. It was created to replace the earlier Exterior Gateway Protocol and to provide a scalable mechanism for interconnecting the rapidly expanding networks managed by different organizations, such as AT&T, Sprint Corporation, and MCI Communications. Its primary function is to facilitate the exchange of network prefix reachability between autonomous systems, which are large blocks of IP addresses controlled by a single administrative entity like an Internet service provider or a major enterprise. The stability of the global Internet depends heavily on the correct operation of this protocol across tens of thousands of these systems.

Technical operation

Sessions are established between peers, known as BGP speakers, using a reliable transport protocol, specifically Transmission Control Protocol on port 179. During a session, speakers exchange messages to open and confirm connection parameters, keep the session alive, send routing updates, and report errors. The most important information exchanged is contained in UPDATE messages, which announce new routes, withdraw unreachable ones, and carry path attributes. Key attributes include the AS_path, which lists the sequence of autonomous systems a route has traversed, the Next Hop, and various metrics used for path selection like Local Preference. The complex decision process for selecting the best path involves analyzing these attributes against policies often set in configurations on routers from vendors like Juniper Networks and Huawei.

Security and reliability

Historically, the protocol relied on implicit trust between peers, making it vulnerable to route hijacking and leaks, which can cause widespread outages or traffic interception. Notable incidents include the 2008 Pakistan Telecom hijack of YouTube traffic and the 2017 Amazon Route 53 incident involving Main One. To improve security, extensions like the Resource Public Key Infrastructure framework, detailed in RFC 6810 and RFC 8205, have been developed to allow cryptographic validation of route origination. Other measures include prefix filtering, described in documents like RFC 7454, and the implementation of the BGP Monitoring Protocol for real-time observation of routing changes by organizations such as the RIPE NCC.

Deployment and versions

The current standard version for use on the IPv4 Internet is BGP-4, codified in RFC 4271. A major extension, Multiprotocol BGP, defined in RFC 4760, added support for other address families, most notably for IPv6 and MPLS VPNs. This extension was crucial for the deployment of the next-generation Internet protocol. While the core protocol has remained stable, ongoing work within the IETF IDR Working Group continues to produce updates, such as RFC 7911 for advertisement of multiple paths, to enhance scalability and operations for large networks like those operated by Google and Facebook.

Role in Internet architecture

It is the glue that binds the Internet's autonomous systems together, making it a critical component of the Internet backbone. Without it, the decentralized, global routing system would not function. Its policies directly influence Internet traffic flow, peering agreements between giants like Comcast and Level 3 Communications, and the implementation of transit services. Major Internet exchange points, such as DE-CIX in Frankfurt and AMS-IX in Amsterdam, rely on it to facilitate efficient peering. Its operation is fundamental to the concept of net neutrality and the geopolitical landscape of Internet routing, as seen in discussions at forums like the Internet Governance Forum.

Category:Internet protocols Category:Routing protocols Category:Internet architecture