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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BGP4 has been in use on the Internet since The Phase 2 function is a separate process, which completes when it has no further work to do. We would like to specially acknowledge numerous contributions by Dennis Ferguson to the earlier version of this document.

Because the mechanism defined in the RFC does not provide peer-entity rgc, these connections may be subject to some forms of replay attacks that will not be detected at the TCP layer. In common practice, [14] only one of the confederation AS numbers is seen by the Internet as a whole.

Examples of common communities include local preference adjustments, geographic or peer type restrictions, DoS avoidance black holingand AS prepending options. They exchange messages to open and confirm the connection parameters. This method also successfully avoids the overhead of bhp flap damping for iBGP sessions.

While this slowed the growth of the routing table to a linear process for several years, with the expanded demand for multihoming by end user networks the growth was once again superlinear by the middle of BGP is an inter-Autonomous System routing protocol. In order to make decisions in its operations with 42771, a BGP peer uses a simple finite state machine FSM that consists of six states: Efficient Organization of Routing Information Having selected the routing information it will advertise, a BGP speaker may avail itself of several methods to organize this information in an efficient manner.



Border Gateway Protocol

To work around this problem, BGP administrators of that multihomed network may divide a large contiguous IP address block into smaller blocks and tweak the route announcement to make different blocks look optimal on different paths, so that external networks will choose a different path to reach different blocks of that multi-homed network. With one address prefix per message there is a substantial increase in overhead in the receiver.

If there is more than one route still tied at this point, several BGP implementations offer a configurable option to load-share among the routes, accepting all or all up to some number. Even simple multihoming can have modest routing table size. This is an advisory qualification to readvertisement of a route prefix, permitting an AS not to readvertise the route prefix to all external bilateral peer neighbour AS’s.

RFC – part 4 of 4

This network reachability information includes information on the list of Autonomous Systems that reachability information traverses. Aggregating Routing Information Aggregation is the process of combining the characteristics of several different routes in such a way that a single route can be advertised.

With damping, a route’s flapping is exponentially decayed.

The neighbor could send several possible routes to a destination, but the first level of preference is at the neighbor level. If an optional attribute is recognized rfx has a valid value, then, depending on the type of the optional attribute, it is processed locally, retained, and updated, if necessary, for possible propagation to other BGP speakers.

Frequency of Route Origination These tools may bbp combined, for example, as a hierarchy of route reflectors. An 4217 to full mesh IBGP. Changing the attribute s of a route is accomplished by advertising a replacement route. A given BGP speaker MAY apply the same jitter to each of these quantities, regardless of the destinations to which the updates are being sent; that is, jitter need not be configured on a per-peer basis.


The Phase 2 decision function is blocked from running while the Phase 3 decision function is in process. AS2 will see the four routes from AS1 Operations of a BGP speaker that is configured to accept routes with its own autonomous system number in the AS path are outside the scope of this document. The BGP Extended Community Attribute was added inin order to extend the range of such attributes and to provide a community attribute structuring by means of a type field. BGP communities are attribute tags that can be applied to incoming or outgoing prefixes to achieve some common goal RFC Keepalive messages are exchanged and, upon successful receipt, the router is placed into the “Established” state.

The new routes appear to have been reaggregated within 5 minutes, but instability across the Internet apparently continued for a number of hours. Implementation Recommendations This section presents some implementation recommendations.

For a multi-homed network, if it announces the same network blocks across all of its BGP peers, the result may be that one or several of its inbound links become congested while the other links remain under-utilized, because external networks all picked that set of congested paths as optimal.

This document is subject to the rights, licenses and restrictions contained in BCP 78and except as set forth therein, the authors retain all their rights. 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.

A single router or two for redundancy can be made a route reflector: If AS1 later decides to drop the route