What are the differences between EIGRP and BGP?

Let us understand the concepts of Enhanced Interior Gateway Routing Protocol (EIGRP) and Border Gateway Protocol (BGP) before learning the differences between them.

Enhanced Interior Gateway Routing Protocol (EIGRP)

EIGRP is the enhanced version of IGRP protocol, incorporating all the features of IGRP while adding significant improvements. It overcomes IGRP's drawbacks including slow convergence, hop count limitations, and lack of Variable Length Subnet Masking (VLSM) support.

In EIGRP, communication with neighboring routers occurs through Hello packets, while information exchange happens via Update packets. The protocol maintains a topology table containing path information and calculates the shortest path using the Diffusing Update Algorithm (DUAL).

EIGRP Metric Calculation

EIGRP uses the following network attributes to calculate metric values:

• Bandwidth − Link capacity

• Delay − Path delay

• Reliability − Link reliability

• Load − Link utilization

The EIGRP metric formula is:

EIGRP Metric = 256 * ((K1*Bandwidth) + (K2*Bandwidth)/(256-Load) + K3*Delay) * (K5/(Reliability + K4))

With default K values (K1=1, K3=1, K2=K4=K5=0), the simplified formula becomes:

EIGRP Metric = 256 * (Bandwidth + Delay)

Border Gateway Protocol (BGP)

BGP is a standardized exterior gateway protocol designed to exchange routing and reachability information between autonomous systems (AS) on the Internet. It is classified as both a path vector protocol and a distance-vector routing protocol.

BGP operates by establishing peering relationships between routers in different autonomous systems. It automatically determines the best path for data transmission based on various attributes and policies configured by network administrators.

BGP Characteristics

• Path information − Maintains complete AS path information

• Policy support − Allows complex routing policies

• Runs over TCP − Uses reliable TCP connection (port 179)

• Incremental updates − Sends only routing changes

EIGRP vs BGP Comparison

Key Use Cases

EIGRP is ideal for enterprise networks requiring fast convergence and efficient routing within a single administrative domain. It excels in campus networks and corporate WANs where Cisco equipment predominates.

BGP is essential for Internet service providers, large enterprises with multiple AS connections, and any organization requiring policy-based routing between autonomous systems. It handles global Internet routing and multi-homing scenarios.

Conclusion

EIGRP serves as an efficient interior gateway protocol for single autonomous systems, while BGP handles inter-AS routing across the Internet. EIGRP offers fast convergence within organizations, whereas BGP provides scalable, policy-driven routing between different administrative domains.