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.

Author: Shakazshura Goltilkis
Country: Madagascar
Language: English (Spanish)
Genre: Science
Published (Last): 23 June 2008
Pages: 148
PDF File Size: 12.50 Mb
ePub File Size: 8.81 Mb
ISBN: 873-2-37144-121-1
Downloads: 51692
Price: Free* [*Free Regsitration Required]
Uploader: Shaktisida

For example, a directly connected prefix, learned from the router’s own hardware, is usually most preferred. While a full IPv4 BGP table as of August [update]is in excess ofprefixes, [22] many older routers have a limit of k ,—, [23] [24] routing table entries. 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.

Views Read Edit Bgpp history.

Border Gateway Protocol BGP is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems AS on the Internet. This mechanism consists of a set of rules.

This article’s lead section does not adequately summarize key points of its bg. In the latter case the route selection process moves to the next tie breaker. This technique does not increase the number of routes seen on the global BGP table.

The current standard however specifies that missing MEDs are to be treated as the lowest possible value.

At the first instance when a route becomes unavailable and quickly reappears, damping does not take effect, so as to maintain the normal fail-over times of BGP. In the network as a whole it is normal for these changes to happen almost continuously, but for any particular router or link, changes are supposed to be relatively infrequent.

Other deployment topologies are also possible, such as running eBGP peering inside a VPN tunnel, allowing two remote sites to exchange routing information in a secure and isolated manner. Increasingly, BGP is used as a generalized signaling protocol to carry information about routes that may not be part of the global Internet, such as VPNs.


Information on RFC » RFC Editor

How routes are propagated can be controlled in detail via the route-maps mechanism. This requires a reboot on most routers.

Rrfc actually carried the information with which rules inside BGP-speaking routers could make policy decisions. In the “Connect” state, the router waits for the TCP connection to complete and transitions to the “OpenSent” state if successful.

This all counts as AS1 announcing four routes. 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. 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. 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.

Confederations can be used in conjunction with route reflectors. If the router does not have a route to that destination from any non-BGP source, the efc route will be removed from the main routing table. Retrieved 13 April Confederations are used in very large networks where a large AS can be configured to encompass smaller more manageable internal ASs. 17771 all ISPs give out their communities to the public, while some other do.

The action could be to drop the route, or it could be to modify some attributes of the route before inserting it in the routing table. 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 We show that the current damping design leads to the intended behavior only under persistent route flapping.


The neighbor could send several possible routes to a destination, but the first level of preference is at the neighbor level. The BGP design is such that delivery of traffic may not function while routes are being updated.

Border Gateway Protocol

This article’s Criticism or Controversy section may compromise the article’s neutral point of view of the subject. Retrieved from ” https: With damping, a route’s flapping is exponentially decayed. Thus, it allows a multicast routing topology different from the unicast routing topology. However, a bit in the type field within the attribute decides whether the encoded extended community is of a transitive or non-transitive nature. BGP4 has been in use on the Internet since This pattern of repeated withdrawal and re-announcement known as route flapping can cause excessive activity in all the other routers that know about the broken link, as the same route is continually injected and withdrawn from the routing tables.

By using this site, you agree to the Terms of Use and Privacy Policy. 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 route-propagation rules effectively require that all iBGP peers inside an AS are interconnected in a full mesh.