What is EIGRP?
Why Interviewers Ask This
This question targets practical, hands-on experience with Networking. Interviewers want to see if you've worked with these concepts in real projects, not just read about them. Strong answers include concrete examples.
Answer
EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco-proprietary advanced distance-vector routing protocol that uses features of both distance-vector and link-state protocols. It is often called a "hybrid" or "balanced hybrid" protocol. EIGRP uses the DUAL (Diffusing Update Algorithm) to calculate loop-free paths and maintain backup routes (feasible successors) so it can instantly switch to a backup path without waiting for reconvergence. EIGRP sends partial, bounded updates only when the topology changes (not periodic full table updates like RIP), making it bandwidth-efficient. The composite metric uses bandwidth, delay, reliability, and load (by default only bandwidth and delay). EIGRP maintains three tables: neighbor table (adjacent routers), topology table (all learned routes), and routing table (best paths). It supports VLSM, CIDR, and supports IPv4, IPv6, and other Layer 3 protocols. EIGRP converges faster than OSPF in most scenarios and is simpler to configure for smaller networks.
Pro Tip
This topic has Networking-specific nuances that differ from general programming. Highlighting those nuances in your answer shows expertise rather than generic knowledge.