Exterior Gateway Protocols EGP
Routing protocols called Exterior Gateway Protocols (EGPs) are used to transfer routing data between various autonomous systems (ASes). In essence, an autonomous system is a network or collection of networks governed by a single administrative authority. Because they enable communication and the sharing of reachability data between these disparate networks, EGPs are essential for the worldwide routing of traffic over the internet.
The Border Gateway Protocol (BGP) is the most widely utilized Exterior Gateway Protocol at the moment. Because of its shortcomings, the original Exterior Gateway Protocol (EGP) was superseded by BGP, which is now outdated.
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Autonomous Systems (ASes)
The Autonomous System (AS) is a key idea in EGPs. A network or collection of networks under a single administrative control is called an AS. One organisation, business, or governmental body, like a university or an Internet service provider (ISP), may be in charge of running the internetwork. The Autonomous System Number (ASN) of every AS is distinct.
Purpose and Distinction from Interior Gateway Protocols (IGPs)
EGPs are mostly used to exchange information about routes within a number of autonomous systems in order to facilitate traffic flow between them. They are essential for routing between various ISPs or for connecting an enterprise’s network to the internet.
EGPs function at the inter-domain level (between ASes), in contrast to Interior Gateway Protocols (IGPs), which manage routing within a single AS. The word “gateway” in IGP and EGP comes from the historical usage of the term to refer to routers.
Development and Important Protocols
Although the term “EGP” has historically been used to refer to a broad class of protocols, Exterior Gateway Protocol (EGP) is an earlier, more specialized protocol.
The EGP (Obsolete) Original:
- Created in the early 1980s by Bolt, Beranek, and Newman, and RFC 904 (1984) contained the full specifications.
- Reachability was intended to be communicated to and from the core routers of the Advanced Research Projects Agency Network (ARPANET).
- EGP did not take metrics into account when determining the optimal path; instead, it concentrated on network reachability.
- Establishing neighbours, determining their status, and alerting neighbours of reachable networks within their AS were among its primary duties.
Limitations: EGP only supported a tree-like architecture (no loops were permitted), making it extremely basic but constrained. It was less effective since it was unable to keep up with the expansion of the contemporary internet and did not handle multipath networking setups. Scalability was also hindered by its centrally managed design.
Status: Because of its shortcomings, it has since become outdated and been superseded by BGP.
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Define border gateway protocol
The most widely used exterior gateway protocol at the moment is BGP. Large corporations and internet service providers utilize it as their primary route advertising protocol. The first EGP’s work directly led to the development of the current BGP.
How BGP Works
As a path-vector routing protocol, BGP functions. This implies that when routers communicate, they share the complete path the series of independent systems a route has passed through rather than merely the “distance” to a destination, as other interior gateway protocols do. Routing policy implementation and loop prevention depend on this path information.
This is a condensed explanation of how BGP functions:
Autonomous Systems (ASes)
There are numerous autonomous systems on the internet. The Autonomous System Number (ASN) of every AS is distinct.
Peering
BGP routers, which are frequently found at an AS’s edge, connect directly to BGP routers in other ASes through a process known as peering or neighbour relationships. TCP on port 179 is usually used for this.
Route Exchange
BGP routers share routing data after establishing a peering session. Network prefixes, or IP address ranges, and a collection of path attributes are included in this data.
Path Attributes
These characteristics offer comprehensive details about a route, including:
- AS_PATH: The list of ASNs that the route has traversed. In order to steer clear of unduly lengthy routes, BGP favors shorter AS_PATHs.
- NEXT_HOP: The router’s IP address that will arrive at the destination next.
- Within an AS, LOCAL_PREF is used to affect the flow of outgoing traffic.
- Multi-Exit Discriminator, or MED, is used to affect the flow of incoming traffic from external ASes.
- And a number of others that aid in choosing a path.
Best Path Selection
A BGP router employs a sophisticated algorithm that assesses these path attributes in order to choose the “best” path when it gets numerous routes to the same location. Network administrators can control how traffic enters and exits their network through this policy-driven procedure.
Policy Enforcement
BGP’s capacity to enforce routing policies is one of its primary features. Administrators can set up rules to regulate which routes are promoted to neighbours, affect traffic flow, and favour some routes over others.
Scalability
BGP is built to be extremely scalable, meaning it can manage the enormous volume of routes on the worldwide internet. To effectively handle this scale, it makes advantage of incremental updates and route aggregation.
BGP functions as the internet’s “postal service” by determining the most effective and legally compliant method of sending data packets between wildly disparate networks.
IPv6 Support
An extension known as Multiprotocol BGP version 4 (MP BGP-4) added IPv6 capability to Border Gateway Protocol (BGP) version 4, which was intended to be extremely extensible. Like their IPv4 predecessors, IPv6 routing protocols adhere to the same EGP principles.
Use Cases
EGPs are necessary because:
- Big Hierarchical Networks: Global networks, such as the Internet, are examples of huge hierarchical networks that EGPs can work with.
- Multiple Administrative Units: An EGP, such as BGP, is used for routing between various autonomous systems when a business has multiple locations, each of which has its own administrative unit.
- Dual-homed Connections: When two Internet Service Providers (ISPs) have a dual-homed connection, such as when routing between the Internet and Internet 2, an EGP like BGP is required.
EGPs, namely BGP, function as the internet’s “postal service” by determining the most effective and legally compliant method of sending data packets between wildly disparate networks.
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