An Interior Gateway Protocol (IGP) is a routing protocol used to exchange routing data within an autonomous system.
Understanding Interior Gateway Protocols (IGPs)
An IGP's primary function is to dynamically learn and maintain the best paths for routing network traffic within a single administrative domain, like a corporate network or an internet service provider's (ISP) internal network. This contrasts with Exterior Gateway Protocols (EGPs), such as BGP, which handle routing between different autonomous systems.
Key Characteristics of IGPs:
- Operate Within an Autonomous System: IGPs are designed for routing within a single, controlled network environment.
- Dynamic Routing: IGPs automatically adjust routing tables based on network changes (e.g., link failures, new devices). This ensures efficient and reliable data delivery.
- Routing Table Exchange: They facilitate the exchange of routing information between routers, allowing each router to build a map of the network topology.
- Path Selection: IGPs utilize various metrics and algorithms to determine the "best" path for data to travel, considering factors like hop count, bandwidth, delay, and cost.
Common IGP Examples:
| Protocol | Description |
|---|---|
| RIP (v1 & v2) | Routing Information Protocol. An older distance-vector protocol, simple to configure but limited in scalability and convergence speed. |
| OSPF (v2 & v3) | Open Shortest Path First. A widely used link-state protocol known for its efficient convergence and scalability. |
| EIGRP | Enhanced Interior Gateway Routing Protocol. A Cisco proprietary hybrid protocol, offering fast convergence and efficient use of network resources. |
| IS-IS | Intermediate System to Intermediate System. Another link-state protocol, often used in large service provider networks. |
IGP vs. EGP:
| Feature | IGP (Interior Gateway Protocol) | EGP (Exterior Gateway Protocol) |
|---|---|---|
| Scope | Routing within an autonomous system (AS) | Routing between autonomous systems (ASs) |
| Example | OSPF, RIP, EIGRP, IS-IS | BGP (Border Gateway Protocol) |
| Focus | Optimizing routing within a controlled network | Establishing routing policies and reachability between networks |
| Administrative Control | Single administrative domain | Multiple administrative domains |
In summary, IGPs are essential for enabling efficient and dynamic routing within a network, ensuring data packets reach their destination through the best available paths. They form the backbone of routing within private networks, corporate environments, and service provider infrastructures.
