A Border Gateway Protocol 4 (BGP-4), January Canonical URL: https:// ; File formats: Plain Text PDF; Status: DRAFT. Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to RFC corrected errors, clarified ambiguities and updated the. RFC (part 1 of 4): A Border Gateway Protocol 4 (BGP-4).
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BGP, Border Gateway Protocol
Network Working Group Y. Please refer to the current edition of the “Internet Official Protocol Standards” STD 1 for the standardization state and status of this protocol. Distribution of this memo is unlimited. This network reachability information includes information on the list of Autonomous Systems ASes that reachability information traverses. This information is sufficient for constructing a graph of AS connectivity for this reachability from which routing loops may be pruned, and, at the AS level, some policy decisions may be enforced.
Border Gateway Protocol
These mechanisms include support for advertising a set of efc as an IP prefix, and eliminating the concept of network “class” within BGP. BGP-4 also hgp mechanisms that allow aggregation of routes, including aggregation of AS paths. This document obsoletes RFC Table rcc Contents 1. Definition of Commonly Used Terms Message Header Error Handling Hold Timer Expired Error Handling Finite State Machine Error Handling Terms “active” and “passive” FSM and Collision Detection Calculation of Degree of Preference Breaking Ties Phase Controlling Routing Traffic Overhead Frequency of Route Advertisement Frequency of Route Origination Efficient Organization of Routing Information Comparison with RFC Multiple Networks Per Message Control Over Version Negotiation This information is sufficient for constructing a graph of AS connectivity for this reachability, from which routing loops may be pruned and, at the AS level, some policy decisions may be enforced.
These mechanisms include support for advertising a set of destinations as an IP prefix and eliminating the concept of network “class” within BGP.
Routing information exchanged via BGP supports only the destination- rfx forwarding paradigm, which assumes that a router forwards a packet based solely on the destination address carried in the IP header of the packet. This, in turn, reflects the set of policy decisions that can and cannot be enforced using BGP.
BGP can support only those policies conforming to the destination-based forwarding paradigm. Definition of Commonly Used Terms This section provides definitions for terms that have a specific meaning to the BGP protocol and that are used throughout the text. Autonomous System AS The classic definition of an Autonomous System is a set of routers under a single technical administration, using an interior gateway protocol IGP and common metrics to determine how to route packets within the AS, and using an inter-AS routing protocol to determine how to route packets to other ASes.
Since this classic definition was bhp, it has become common for a single AS to. The use of the term Autonomous System stresses the fact that, even when multiple IGPs and metrics are used, the administration of an AS appears to other ASes to have a single coherent interior routing plan, and presents a consistent picture of the destinations that bbgp reachable through it. External peer Peer that is in a different Autonomous System than the local system.
Feasible route An advertised route that is available for use by the recipient. Internal peer Peer that is in the same Autonomous System as the local system. IGP Interior Gateway Protocol – a routing protocol used to exchange routing information among routers within a single Autonomous System. Route A unit of information that pairs a set of destinations with the attributes of a path to those destinations. Unfeasible route A previously advertised feasible route that is no longer available for use.
RFC A Border Gateway Protocol 4 (BGP-4) – Wikidata
Honig for their contributions to the earlier version BGP-1 of this document. We would like to specially acknowledge numerous contributions by Dennis Ferguson to the earlier version of this document.
We would like to explicitly thank Bob Braden for the review of the earlier version BGP-2 of this document, and for his constructive and valuable comments. Johns, and Paul Tsuchiya, acted with frc strong combination of toughness, professionalism, and courtesy.
We would like to specially acknowledge Andrew Lange for his help in preparing the final version of this document. Finally, we would like to thank all the members of the IDR Working Group for their ideas and the support they have given to this document. This information is sufficient for constructing a graph of AS connectivity, from which routing loops may ngp pruned, and, at the AS level, some policy decisions may be enforced.
In the context of this document, we assume that a BGP speaker advertises to its peers only those routes efc it uses itself in this context, a BGP speaker is said to “use” a BGP route if it is the most preferred BGP route and is used 42271 forwarding. All other cases are outside the scope of this document.
Note that some policies cannot be supported by the destination-based forwarding paradigm, and thus require techniques such as source routing aka explicit 4217 to be enforced. Such policies cannot be enforced using BGP either. On the other hand, BGP can support any policy conforming to the destination-based forwarding paradigm. These mechanisms include support for advertising a set of destinations rfv an IP prefix and eliminating the concept of a network “class” within BGP.
The classic definition of an Autonomous System is a set of routers under a single technical administration, using an interior gateway protocol IGP and common metrics to determine how to route packets within the AS, and using an inter-AS routing protocol to determine how to route packets to other ASes.
Since this classic definition was developed, it has become rfv for a single AS to use several IGPs and, sometimes, several sets of metrics within an AS. The use of the term Autonomous System stresses the fact that, even when multiple IGPs and metrics are used, the administration of an AS appears to other ASes to have a single coherent interior bfp plan and presents a consistent picture of the destinations that are reachable through it.
This eliminates the need to implement explicit update fragmentation, retransmission, acknowledgement, and sequencing. A TCP connection is formed between two systems. They exchange messages to open and confirm the connection parameters.
The initial data flow is the portion of the BGP routing table that is allowed by the export policy, 42711 the Adj-Ribs-Out see 3.
Incremental updates are sent as the routing tables change. BGP does not require a periodic refresh 421 the routing table. A peer in a different AS is referred to as an external peer, while a peer in hgp same AS is referred to as an internal peer. If a particular AS has multiple BGP speakers and is providing transit service for other ASes, then care must be taken to ensure a consistent view of routing within the AS.
Bgl document specifies the base behavior of the BGP protocol. This behavior can be, and is, modified by extension specifications. When the protocol is extended, the new behavior is fully documented in the extension specifications. Advertisement and Storage For the purpose of this protocol, a route is defined as a unit of information that pairs a set of destinations with the attributes of a path to those destinations.
If a BGP speaker chooses to advertise a previously received route, it MAY add to, or modify, the path attributes of the route before advertising it to a peer. BGP provides mechanisms by rc a BGP speaker can inform its peers that a previously advertised route is no longer available for use.
Supported Standards for BGP
There are three methods by which a given BGP speaker can indicate that a route has been withdrawn from service: Changing the attribute s of a route is accomplished by advertising a replacement route.
The replacement route carries new changed attributes and has the same address prefix as the original route. Their contents represent routes that are available as input to the Decision Process.
These are the routes that will be used by the local BGP speaker. The choice of implementation for example, 3 copies of the information vs 1 copy with pointers is not constrained by the protocol.
Routing information that the BGP speaker uses to forward packets or to construct the forwarding table used for packet forwarding is maintained in the Routing Table. The Routing Table accumulates routes to directly connected networks, static routes, routes learned from the IGP protocols, and routes learned from BGP. Whether a specific BGP route should be installed in the Routing Table, and whether a BGP route should override a route to the same destination installed by another source, is a local policy decision, and is not specified in this document.
In addition to actual packet forwarding, the Routing Table is used for resolution of the next-hop addresses specified in BGP updates see Section 5.