EGP in networking stands for Exterior Gateway Protocol, a routing protocol used to exchange routing data between different autonomous systems.
Understanding Exterior Gateway Protocol (EGP)
EGP is a protocol designed for exchanging routing information between gateway hosts in different autonomous systems. An autonomous system is a collection of networks under a common administration. EGP allows routers in different autonomous systems to learn about the reachability of networks in other autonomous systems.
Key Characteristics:
- Routing Protocol: EGP functions as a routing protocol. This means it facilitates the exchange of network reachability information.
- Autonomous Systems: It specifically operates between different autonomous systems. This is its primary differentiating factor from Interior Gateway Protocols (IGPs).
- Reachability Information: EGP primarily exchanges reachability information, which helps routers determine the best path to a destination network.
- Simplicity: Compared to modern routing protocols, EGP is relatively simple.
How EGP Works (Simplified):
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Neighbor Discovery: EGP relies on preconfigured neighbors. Routers must be explicitly configured to peer with other routers in different autonomous systems.
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Reachability Exchange: Once a neighbor relationship is established, routers periodically exchange reachability updates. These updates inform each router about the networks reachable through the sending router.
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Path Determination: Routers use the received reachability information to build their routing tables. This allows them to forward traffic towards destination networks in other autonomous systems.
Limitations of EGP
EGP has significant limitations that led to its obsolescence. These include:
- Limited Metric: EGP only used a simple "reachable/unreachable" metric. It lacked support for cost or path selection, making it difficult to choose the best route.
- Tree-Based Topology: EGP assumed a tree-like topology, which is not suitable for the complex, meshed networks of today's Internet.
- No Loop Detection: EGP lacked built-in loop detection mechanisms, potentially leading to routing loops.
Replacement by BGP
Due to these limitations, EGP has been superseded by the Border Gateway Protocol (BGP). BGP is a more sophisticated and scalable routing protocol that addresses the shortcomings of EGP. BGP supports policy-based routing, path selection, and loop detection, making it a more suitable choice for inter-autonomous system routing.
EGP vs. IGP
| Feature | EGP | IGP |
|---|---|---|
| Scope | Between Autonomous Systems | Within an Autonomous System |
| Purpose | External Routing | Internal Routing |
| Metric | Simple Reachability | Cost-based, Sophisticated Metrics |
| Complexity | Relatively Simple | Can be Simple or Complex |
| Example | Obsolete, replaced by BGP | RIP, OSPF, EIGRP |
| Current Usage | No longer used | Widely used within networks |
In summary, EGP was an early exterior routing protocol used to exchange routing information between different autonomous systems, but it has been replaced by more advanced protocols like BGP due to its limitations.
