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See: 4271 on datatracker.ietf.org

The title of this RFC is “Border Gateway Protocol 4 (BGP-4).”

RFC 4271 defines the fourth version of the Border Gateway Protocol (BGP-4), which is the standard protocol used for inter-domain routing on the internet. BGP is a path-vector routing protocol that manages the exchange of routing information between autonomous systems (AS), ensuring that data can be efficiently routed across diverse and distributed networks. BGP-4 allows for the aggregation of routes and supports Classless Inter-Domain Routing (CIDR), which helps reduce the size of routing tables and conserves IP address space. The related RFC is RFC 4271, which provides detailed specifications for the operation and management of BGP-4 across the global internet. https://en.wikipedia.org/wiki/Border_Gateway_Protocol https://tools.ietf.org/html/rfc4271

One of the key features of BGP-4 is its ability to maintain multiple paths for a given destination, allowing networks to optimize traffic flows based on various policies and preferences. By using attributes such as AS path length, next-hop, and local preference, BGP can make flexible routing decisions that suit the needs of different network operators. This flexibility is essential for large networks like Internet Service Providers (ISPs) and enterprises that need to maintain efficient and resilient connectivity. The related RFC is RFC 4271, which outlines how BGP routers exchange routing information and make decisions based on path attributes. https://en.wikipedia.org/wiki/Autonomous_system_(Internet) https://tools.ietf.org/html/rfc4271

Another significant aspect of BGP-4 is its support for route aggregation and CIDR. Prior to the introduction of CIDR, IP addresses were assigned based on classful addressing, which often led to inefficient allocation of address space. With CIDR, BGP-4 can aggregate multiple IP prefixes into a single route advertisement, reducing the number of routes that must be maintained by BGP routers. This feature has been critical in addressing the scalability challenges of the growing internet. The related RFC is RFC 1519, which introduced CIDR and its implementation in BGP-4 to improve the efficiency of IP routing. https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing https://tools.ietf.org/html/rfc1519

BGP-4 operates over TCP to ensure reliable delivery of routing information between peers. Each BGP session is established over a TCP connection, allowing BGP messages to be exchanged reliably. If the TCP session fails, the BGP connection is terminated, and the routers must reestablish the session to resume the exchange of routing information. This reliance on TCP provides BGP with a stable and reliable transport mechanism, which is essential for ensuring accurate and consistent routing updates. The related RFC is RFC 793, which defines TCP and its use in reliable data transmission for BGP and other protocols. https://en.wikipedia.org/wiki/Transmission_Control_Protocol https://tools.ietf.org/html/rfc793

BGP-4 also includes mechanisms for detecting and responding to routing loops, which can cause traffic to be misrouted or dropped. The AS path attribute, which lists all the autonomous systems that a route has traversed, is used to detect loops. If a BGP router receives an update that contains its own AS in the AS path, it discards the route, preventing a loop from occurring. This ensures that traffic is routed efficiently and avoids unnecessary delays caused by loops. The related RFC is RFC 4271, which specifies how BGP routers handle loop detection and prevention. https://en.wikipedia.org/wiki/Routing_loop https://tools.ietf.org/html/rfc4271

BGP-4 is also highly extensible, allowing for the introduction of new features and capabilities without requiring significant changes to the protocol. One example of this extensibility is Multiprotocol BGP (MP-BGP), which enables BGP to carry routing information for multiple network layer protocols, such as IPv6 or MPLS. This extensibility has made BGP a versatile protocol, capable of supporting the evolving needs of the global internet. The related RFC is RFC 4760, which defines MP-BGP and its role in supporting multiple protocols over a BGP session. https://en.wikipedia.org/wiki/Multiprotocol_Extensions_for_BGP-4 https://tools.ietf.org/html/rfc4760

One of the challenges with BGP-4 is its vulnerability to security threats, such as route hijacking and misconfigurations that can lead to widespread outages. To address these concerns, several security enhancements have been proposed, including BGP origin validation and BGP route filtering. These measures help ensure that only authorized routes are advertised and accepted, improving the security and stability of BGP routing. The related RFC is RFC 6811, which introduces BGP origin validation to protect against route hijacking by verifying the legitimacy of AS announcements. https://en.wikipedia.org/wiki/BGP_hijacking https://tools.ietf.org/html/rfc6811

The title of this RFC is “Border Gateway Protocol 4 (BGP-4).” RFC 4271 provides the foundational framework for inter-domain routing on the internet, allowing BGP-4 to manage the exchange of routing information between autonomous systems. With features like route aggregation, loop prevention, and extensibility through Multiprotocol BGP, BGP-4 has become an essential protocol for maintaining efficient, scalable, and reliable connectivity across diverse networks. Despite security challenges, ongoing enhancements such as BGP origin validation help secure the protocol's operation. RFC 4271 remains a critical document for understanding and implementing BGP in the global internet.