Border Gateway Protocol > Advanced

From Citizendium, the Citizens' Compendium

A number of advanced BGP protocol functions have been developed to improve the scalability, robustness, and security of BGP. This page introduces them; see feature-specific articles for additional details and applications.

Contents 1 iBGP scalability 1.1 Route reflector 1.2 Confederations for scalability 2 eBGP scalability 2.1 ORF 2.2 route servers 3 Policy signaling 3.1 Confederations for policy 4 Route selection algorithm 5 Security architecture 5.1 Trusted registries 6 References

iBGP scalability

One of the major scalability problems of BGP over TCP, which can be tuned on a local basis, is that TCP takes a substantial amount of processing, as can the per-interface issues of BGP setup, advertising, and acceptance. Two techniques, route reflectors and confederations can reduce the need for the high overhead of full meshing. The methods can be used in conjunction wit one another.

Both major techniques can suffer from instability ^[1] unless you use an OSPF-like rule. In OSPF, intra-area routes are always preferred, regardless of metric. The equivalent, for avoiding oscillation, is always to prefer cluster-local or confederation-internal routes.

Route reflector

The basic rule of iBGP is that all BGP speakers within an AS must peer with one another, which leads to an exponential growth of BGP sessions. Session maintenance, both of the BGP session proper and the TCP connection over which it runs, are processor-intensive and may require more powerful router control plane hardware.

BGP route reflectors introduce hierarchy, a well-recognized means of scaling, into iBGP. Route reflector clusters have at least one route reflector that acts as a server to other iBGP speakers within the cluster, and some number of route reflector clients. There must be full iBGP meshing inside the cluster, but only the route reflector server needs to peer, via iBGP, with other iBGP speakers (including other clusters) inside the AS. ^[2]

Confederations for scalability

eBGP scalability

ORF

route servers

Policy signaling

BGP communities are attributes that can be used to identify a related group of routes.^[1] There are both well-known communities that should be recognized by all BGP implementations, and various kinds of communities that are usually defined by an autonomous system ^[3]

To deal with Internet growth and the use of BGP in intranets and extranets (e.g., virtual private networks), various extended communities have been defined. ^[4]

Confederations for policy

BGP confederations are sets of autonomous systems, as distinct from communities, which are sets of routes.^[5] In practice, confederations are most often used as ways to get finer policy granularity within an autonomous system visible on the Internet. For example, if AS number 1 is visible, it might internally use AS 64000, 64001, and 64002 to impose policies relevant to its internal routing flow.

Route selection algorithm

• Load balancing specifics

Security architecture

• Also see BGP/Operations

Trusted registries

References