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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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BGP4 has been in use on the Internet since If a given route is withdrawn by a neighbor, and there is no other route to that destination, the route is removed from the Loc-RIB, and no longer sent, by BGP, to the main routing table manager. This method also successfully avoids the overhead of route flap damping for iBGP sessions.

In the “OpenSent” state, the router sends an Open message and waits for one in return in order to transition to the “OpenConfirm” state.

The BGP defines the messages that each peer should exchange in order to change the session from one state to another. The BGP design is such that delivery of traffic may not function while routes are being updated. The end user has no technical ability to enforce correct actions being taken by the ISP, though problems in this area are generally rare and accidental.

The k 1771 was predicted in advance by a number of IT professionals.

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

During the peering handshake, when OPEN messages are exchanged, BGP speakers can negotiate [7] optional capabilities of the session, including multiprotocol extensions and various recovery modes. Route reflectors [13] reduce the number of connections required in an AS. With the introduction of 32 bits AS numbers, some issues were immediately obvious with the community attribute that only defines a 16 bits ASN field, which prevents the matching between this field and the real ASN value.

However, a bit in the type field within the attribute decides whether the encoded extended community is of a transitive or non-transitive nature.


A BGP speaker sends byte keep-alive messages every 60 seconds [5] to maintain the connection. 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.

This page was last edited on 5 Decemberat The neighbor could send several possible routes to a destination, but the first level of preference is at the neighbor level. Retrieved from ” https: Please consider expanding the lead to provide an accessible overview of all important aspects of the article.

Routers on the boundary of one AS exchanging information with another AS are called border or edge routers or simply eBGP peers and are typically connected directly, while iBGP peers can be interconnected through other intermediate routers.

Confederations are sets of autonomous systems. This mechanism consists of a set of rules. In the “Connect” state, the router waits for the TCP connection to complete and transitions to the “OpenSent” state if successful. If flap damping is implemented, the ISP operating that network will cause side-effects to their customers and the Internet users of their customers’ content and services The current standard however specifies that missing MEDs are to be treated as the lowest possible value.

BGP communities are attribute tags that can be applied to incoming or outgoing prefixes to achieve some common goal RFC Route reflectors are a pure performance-enhancing technique, while confederations also can be used to implement more fine-grained policy.

Views Read Edit View history. This technique does not increase the number of routes seen on the global BGP table. 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.

BGP-4 – Border Gateway Protocol 4 (RFC ) | AcronymFinder

This full-mesh configuration requires that each router maintain a session to every other router. If AS2 wants to send data to prefix Without damping, the excessive activity can cause a heavy processing load on routers, which may in turn delay updates on other routes, and so affect overall routing stability.


Until recently, it was a common mistake to say BGP carries policies. This pattern of repeated withdrawal and re-announcement known as route flapping can cause excessive activity in all the other routers that know 171 the broken link, as the same route is continually injected and withdrawn from the routing tables.

Border Gateway Protocol

If the router does not have a route to that destination from any non-BGP source, the withdrawn route will be removed from the main routing table. When the number of flaps is small, the global routing dynamics deviates significantly from the expected behavior with a longer convergence delay. Their structure is not visible to other BGP routers, although they usually can be interrogated with management commands on the local router.

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. Bg;, for each neighbor, the BGP process applies various standard and implementation-dependent criteria to decide which routes conceptually should go into the Adj-RIB-In.

This article’s lead section does not adequately summarize key points of its contents. If one router implementation takes more memory per route than another implementation, this may be a legitimate design choice, trading processing speed ngp memory. These side-effects would quite likely be worse than the impact caused by simply bggp running flap damping at all. MEDs, defined in the main BGP standard, were originally intended to show to another bp AS the advertising AS’s preference as to which of several links are preferred for inbound traffic.

For each bggp session, a BGP implementation maintains a state variable that tracks which of these six states the session is in.

These route-propagation rules effectively require that all iBGP peers inside an AS are interconnected in a full mesh.