EIGRP (Enhanced Interior Gateway Routing Protocol) is used primarily for routing within enterprise networks. It is designed to provide fast convergence, low overhead, and support for a variety of network topologies. EIGRP is particularly advantageous in large-scale networks where rapid and efficient routing updates are crucial for maintaining network performance and reliability.
EIGRP and OSPF (Open Shortest Path First) are both interior gateway protocols used for routing within autonomous systems. However, they differ in their operation and characteristics. EIGRP uses a hybrid approach that incorporates aspects of both distance vector and link-state routing protocols. It maintains a topology table similar to link-state protocols while calculating routes based on distance and metric updates similar to distance vector protocols. OSPF, on the other hand, strictly follows the link-state routing protocol model, where routers exchange detailed information about network topology using link-state advertisements (LSAs).
EIGRP is considered a hybrid routing protocol because it combines features of both distance vector and link-state routing protocols. Unlike traditional distance vector protocols, EIGRP uses Diffusing Update Algorithm (DUAL) to calculate the shortest path to a destination based on bandwidth, delay, reliability, load, and MTU. This allows EIGRP to converge quickly while reducing the potential for routing loops and ensuring efficient use of network resources.
EIGRP is a classless routing protocol. Unlike classful routing protocols that only support classful subnet masks (e.g., RIP version 1), EIGRP supports variable-length subnet masks (VLSM) and classless inter-domain routing (CIDR). It can advertise and route to subnets of different sizes within the same major network, providing flexibility and efficient use of IP address space. This classless behavior allows EIGRP to support modern network architectures and subnetting schemes effectively.