A Border Gateway Protocol 4 (BGP-4), March Canonical URL: https://www. ; File formats: Plain Text PDF; Status: DRAFT. Connected: An Internet Encyclopedia RFC RFC Network Working Group Request for Comments: A Border Gateway Protocol 4 (BGP-4). RFC A Border Gateway Protocol 4 (BGP-4) (Q). request for comments publication. RFC; A Border Gateway Protocol 4.

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Thus, it allows a multicast routing topology different from the unicast routing topology. Route reflectors [13] reduce the number of connections required in an AS. If so, it replaces them. One of the largest problems faced by BGP, and indeed the Internet infrastructure as a whole, is the growth of the Internet routing table. The customer simply adjusts their configuration to include the correct community or communities for each route, and the ISP is responsible for controlling who the prefix is advertised to.

To alleviate the problem, BGP implements two options: Outages Possible Next Week”. If AS2 wants to send data to prefix This can then be extended further with features like Cisco’s dmzlink-bw which enables a ratio of traffic sharing based on bandwidth values configured on individual links.

In the “Active” state, the router resets the ConnectRetry timer to zero and returns ggp the “Connect” state. If a router is misconfigured or mismanaged then it may get into a rapid cycle between down and up states.

The BGP defines the messages that each peer should exchange in order to change the session from one state to another. For other uses, see BGP disambiguation. Retrieved March 16, This article’s lead section does not adequately summarize key points of its contents.

The BGP design is such that delivery of traffic may not function while routes are being updated. MEDs, defined in the main BGP standard, were originally intended to show to another neighbor AS the advertising AS’s preference as to which of several links are preferred for inbound traffic.


The term view is often used for these different rvc relationships on a dfc router. As long as that directly connected route’s interface is active, the BGP route to the destination will not be put into the routing table.

Retrieved 13 April Due to the extended attribute range, its usage can be manifold. The first decision point for evaluating NLRI is that its next-hop attribute must be reachable rfv resolvable.

However, subsequent research has shown that flap damping can actually lengthen convergence times in some cases, and can cause interruptions in connectivity even when links are not flapping. RFC corrected errors, clarified ambiguities and updated the specification with common industry 1717. 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 ngp that multi-homed network.

Border Gateway Protocol

Damping can also mitigate denial of service attacks; damping timings are highly customizable. Multiprotocol BGP allows information about the topology of IP multicast-capable routers to be exchanged separately from the topology of normal IPv4 unicast routers. The routing tables managed by a BGP implementation are adjusted continually to reflect actual changes in the network, such as links breaking and being restored or routers going down and coming back up.

This article’s Criticism or Controversy section may compromise the article’s neutral point of view of the subject. Such manipulation is outside the scope of the standard but is commonly used. For instance, new routes learned from an eBGP peer are typically redistributed to all iBGP peers as well as all other eBGP peers if transit mode is enabled on the router.


In the latter case the route selection process moves to the next tie breaker. From Wikipedia, the free encyclopedia. The major enhancement was the support for Classless Inter-Domain Routing and use of route aggregation to decrease the size of routing tables.

After the abnormalities have ceased and a suitable length of time has passed for the offending route, prefixes can be reinstated and its slate wiped clean. The actual allocations which pushed the number of routes above k was the announcement of about 15, new routes in short order, starting at Although MBGP enables the exchange of inter-domain multicast routing information, other protocols such as the Protocol Independent Multicast family are needed to build trees and forward multicast traffic.

In the simplest arrangement, all routers within a single AS and participating in BGP routing must be configured in a full mesh: How routes are propagated can be controlled in detail via the route-maps mechanism.

It should also be noted that the rcf attribute is transitive, but communities applied by the customer very rarely bp propagated outside the next-hop AS. Please integrate the section’s contents into the article as a whole, or rewrite the material.

RFC – A Border Gateway Protocol 4 (BGP-4)

The k problem was predicted in advance by a number of IT professionals. In the network as a whole it is normal for these changes to happen almost continuously, rff for any particular router or link, changes are supposed to be relatively infrequent. Once candidate routes are received from neighbors, the Loc-RIB software applies additional tie-breakers to routes to the same destination.