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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This requires a reboot on most routers. For a multi-homed network, if it announces the same network blocks across all of its BGP peers, the result may byp 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.

For instance, new routes learned from an eBGP peer are typically redistributed to all iBGP peers as bg; as all other eBGP peers if transit mode is enabled on the router.

Border Gateway Protocol – Wikipedia

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. This page was last edited on 5 Decemberat While it is common to say that BGP allows an administrator to set policies on how prefixes are handled by ISPs, this is generally not possible, strictly speaking.

Please consider expanding the lead to provide an accessible overview of all important aspects of the article. Once rfx routes are received from neighbors, the Loc-RIB software applies additional tie-breakers to routes to the same destination.

Ngp discuss this issue on the article’s talk page. Until latethe global routing table was growing exponentiallythreatening an eventual widespread breakdown of connectivity.

Border Gateway Protocol

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. How routes are propagated can be controlled in detail via the route-maps mechanism. Both confederations and route reflectors can be subject to persistent oscillation unless specific design rules, affecting both BGP and the interior routing protocol, are followed.

Rfd and Applications” PDF.

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

Next, 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. By using this site, you agree to the Terms of Ngp and Privacy Policy. If one router implementation takes more memory per route than another implementation, this may be a legitimate design choice, trading processing speed against memory. Route summarization is often used to improve aggregation of the BGP global routing table, thereby reducing the necessary table size in routers of an AS.


Damping can also mitigate denial of service attacks; gfc timings are highly customizable.

Confederations can be used in conjunction with route reflectors. The second state is “Connect”. BGP4 has been in use on the Internet since Retrieved March 16, The neighbor could send several possible routes to a destination, but the first level of preference is at the neighbor level.

If so, it replaces them. 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. Depending on the implementation of that process, the BGP route is not necessarily selected. While this slowed the growth of the routing table to bg linear process for several years, with the expanded demand for multihoming by end user networks the rrc was once again superlinear by the middle of To alleviate the problem, BGP implements two options: From Wikipedia, the free encyclopedia.

If unsuccessful, it starts the ConnectRetry timer and transitions to the “Active” state upon expiration.

For example, a directly connected prefix, learned from the router’s own hardware, is usually most preferred. Archived from the original on However, a bit in the type field within the attribute decides whether the encoded extended community is of a transitive or non-transitive nature.

The router may have to keep more than one copy of a route, so it can manage different policies for route advertising and acceptance to a specific neighboring AS. This causes scaling problems, 171 the number of required connections grows quadratically with the number of routers involved. This mechanism consists of a set of rules. The extended format consists of one or two octets for the type field followed by seven or six octets for the respective community attribute content.

Such manipulation is outside the scope of the standard but is commonly used. This allows for automatic and decentralized routing of traffic across the Internet, but it also leaves the Internet potentially vulnerable to accidental or malicious disruption, known as BGP hijacking. In the simplest arrangement, all routers within a 7171 AS and participating in BGP routing must be tfc in a full mesh: In large networks, this number of sessions may degrade performance of routers, due to either a lack of memory, or high CPU process requirements.


The additional information tells the BGP process such things as whether individual entries belong in the Adj-RIBs for specific neighbors, whether the peer-neighbor route selection process made received policies eligible for the Loc-RIB, and whether Loc-RIB entries are eligible to be submitted to the local router’s routing table management process. These devices, however, may be perfectly reasonable and useful when used for BGP routing of some smaller part of the network, such as a confederation-AS representing one of several smaller enterprises that are linked, by a BGP backbone of backbonesor a small enterprise that announces routes to an ISP but only accepts a default route and perhaps a small number of aggregated routes.

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.

In the “OpenSent” state, the router sends an Open message and waits for one in return in order to transition to the “OpenConfirm” state. A BGP speaker sends byte keep-alive messages every 60 seconds [5] to maintain the connection. BGP neighbors, called peers, are established by manual configuration among routers to create a TCP session on port 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.

Since the current rule may cause different behavior than the vendor interpretations, BGP implementations that used the nonstandard default value have a configuration feature 17771 allows the old or standard rule to be selected. While the reported number of IPv6 advertised routes was only about 20k, the number of advertised IPv4 routes reached the default limit, causing a spillover 7171 as routers attempted to compensate for the issue by using slow software routing as opposed to fast hardware routing via Rrc.

On the Internet, a BGP routing change may cause outages for several minutes. This full-mesh configuration requires that each router maintain a session to every other router. In the “Active” state, the router resets the ConnectRetry timer to zero and returns to the “Connect” state. 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.