Design Principles

EIGRP Network Design

Proper EIGRP network design is crucial for scalability, performance, and maintainability. This section covers fundamental design principles and architectural best practices.

Core Design Principles

Hierarchical Design

Organize network into logical layers and boundaries

Summarization

Aggregate routes at appropriate boundaries

Redundancy

Provide multiple paths for fault tolerance

Scalability

Design for growth and future expansion

Hierarchical Network Design

Three-Tier Architecture

    ┌─────────────────────────────────────┐
    │             Core Layer              │
    │  • High-speed switching/routing     │
    │  • Minimal processing               │
    │  • Route summarization              │
    └─────────────────────────────────────┘
                         │
    ┌─────────────────────────────────────┐
    │         Distribution Layer          │
    │  • Policy enforcement              │
    │  • Route filtering                 │
    │  • Redundancy                      │
    │  • Aggregation                     │
    └─────────────────────────────────────┘
                         │
    ┌─────────────────────────────────────┐
    │           Access Layer              │
    │  • End-user connectivity           │
    │  • Basic services                  │
    │  • Stub configurations             │
    └─────────────────────────────────────┘

IP Addressing Strategy

Hierarchical Addressing Plan

Regional Office: 10.1.0.0/16
├── Core Network: 10.1.0.0/20
│   ├── Core Links: 10.1.0.0/24
│   └── Management: 10.1.1.0/24
├── Distribution: 10.1.16.0/20
│   ├── Dist Links: 10.1.16.0/24
│   └── Services: 10.1.17.0/24
└── Access Networks: 10.1.32.0/19
    ├── Branch 1: 10.1.32.0/24
    ├── Branch 2: 10.1.33.0/24
    └── Branch 3: 10.1.34.0/24

Summary Routes:
- Branch → Distribution: 10.1.32.0/19
- Distribution → Core: 10.1.0.0/16
- Core → WAN: 10.1.0.0/16

Summarization Strategy

Strategic Summarization Points

# Access layer to distribution
interface gigabitethernet0/0
 ip summary-address eigrp 100 192.168.1.0 255.255.255.0

# Distribution to core
interface gigabitethernet0/1
 ip summary-address eigrp 100 192.168.0.0 255.255.248.0

# Benefits:
# - Reduces routing table size
# - Improves convergence time
# - Provides stability
# - Reduces query scope

Design Templates

Standard Configuration Template

# Core router template
router eigrp 100
 eigrp router-id [x.x.x.x]
 network [core-networks]
 no auto-summary
 maximum-paths 4

# Distribution router template
router eigrp 100
 eigrp router-id [x.x.x.x]
 network [distribution-networks]
 no auto-summary
 maximum-paths 4
 
interface [uplink-interface]
 ip summary-address eigrp 100 [summary-route] [mask]

# Access router template
router eigrp 100
 eigrp router-id [x.x.x.x]
 eigrp stub connected summary
 network [access-networks]
 no auto-summary
 passive-interface default
 no passive-interface [uplink-interface]

Scalability

EIGRP Scalability

EIGRP scalability depends on proper network design, summarization, and resource management. Understanding scaling limitations and optimization techniques is essential for large networks.

Scalability Factors

Network Size

Number of routers and routes in the network

Topology Table

Memory consumption for route storage

Convergence Time

Time to react to topology changes

Resource Usage

CPU and memory consumption

EIGRP Scaling Limits

Parameter Theoretical Limit Practical Limit Limiting Factor
Neighbors per Router No hard limit 50-100 Memory and CPU
Routes per Router No hard limit 10,000-50,000 Memory consumption
Network Diameter 100 hops 15-20 hops Convergence time
AS Size No limit 200-500 routers Query scope

Summarization for Scalability

Hierarchical Summarization

# Without summarization (poor scalability)
# Each router knows about all 1000 branch networks
# Topology table: 1000 entries per router
# Query scope: entire network

# With summarization (good scalability)
interface serial0/0/0
 ip summary-address eigrp 100 192.168.0.0 255.255.0.0

# Each router knows about 1 summary per region
# Topology table: 10 entries per router
# Query scope: limited to region

Monitoring Scalability

Scalability Metrics

# Monitor topology table size
show ip eigrp topology summary

# Check memory usage
show processes memory | include EIGRP

# Monitor CPU utilization
show processes cpu | include EIGRP

# Check convergence times
show ip eigrp events

# Monitor neighbor count
show ip eigrp neighbors summary

# Check query statistics
show ip eigrp traffic

Security

EIGRP Security

EIGRP security involves authentication, access control, and monitoring to protect against unauthorized access and malicious routing attacks. Proper security implementation is essential for network integrity.

Security Threats

Unauthorized Access

Rogue routers joining the EIGRP domain

Route Injection

Malicious route advertisements

Man-in-the-Middle

Interception and modification of routing updates

Denial of Service

Overwhelming routers with malicious traffic

MD5 Authentication

MD5 Authentication Configuration

# Create key chain
key chain EIGRP_MD5
 key 1
  key-string MySecretKey123
  accept-lifetime 00:00:00 Jan 1 2024 infinite
  send-lifetime 00:00:00 Jan 1 2024 infinite

# Apply to interface
interface serial0/0/0
 ip authentication mode eigrp 100 md5
 ip authentication key-chain eigrp 100 EIGRP_MD5

# Verify authentication
show ip eigrp neighbors detail

SHA-256 Authentication

SHA-256 Authentication Configuration

# Create key chain for SHA-256
key chain EIGRP_SHA256
 key 1
  key-string StrongPassword456
  cryptographic-algorithm hmac-sha-256
  accept-lifetime 00:00:00 Jan 1 2024 infinite
  send-lifetime 00:00:00 Jan 1 2024 infinite

# Apply to interface
interface serial0/0/0
 ip authentication mode eigrp 100 md5
 ip authentication key-chain eigrp 100 EIGRP_SHA256

# SHA-256 provides stronger cryptographic protection

Passive Interface Security

Secure Default Configuration

router eigrp 100
 # Make all interfaces passive by default
 passive-interface default
 
 # Enable EIGRP only on required interfaces
 no passive-interface serial0/0/0
 no passive-interface serial0/0/1
 
 # Network statements
 network 10.0.0.0 0.255.255.255
 network 192.168.1.0 0.0.0.255

# Benefits:
# - Prevents unauthorized neighbor formation
# - Reduces attack surface
# - Simplifies troubleshooting

Security Best Practices

Security Guidelines

  • Enable Authentication: Use MD5 or SHA-256 authentication
  • Implement Key Rotation: Regularly rotate authentication keys
  • Use Passive Interfaces: Secure unused interfaces by default
  • Monitor Security Events: Enable logging and monitoring
  • Segment Networks: Use multiple AS for security isolation

Performance

EIGRP Performance Optimization

EIGRP performance optimization involves tuning timers, managing resources, and implementing efficient network design to achieve optimal convergence times and resource utilization.

Performance Metrics

Convergence Time

Time to adapt to topology changes

CPU Utilization

Processing overhead for EIGRP operations

Memory Usage

Memory consumption for topology table

Bandwidth Usage

Network overhead for EIGRP packets

Convergence Optimization

Timer Optimization

# Aggressive timer settings for fast convergence
interface serial0/0/0
 ip hello-interval eigrp 100 1
 ip hold-time eigrp 100 3

# Benefits:
# - Faster failure detection
# - Quicker convergence
# - Better user experience

# Considerations:
# - Increased CPU usage
# - More network overhead
# - Potential instability on slow links

BFD Integration

Bidirectional Forwarding Detection

# Enable BFD for subsecond failure detection
interface serial0/0/0
 bfd interval 100 min_rx 100 multiplier 3
 ip routing bfd

# Enable BFD for EIGRP
router eigrp 100
 bfd all-interfaces

# Benefits:
# - Subsecond failure detection
# - Hardware-accelerated
# - Protocol-independent
# - Reduced convergence time

Performance Monitoring

Performance Metrics Collection

# Monitor CPU usage
show processes cpu | include EIGRP

# Check memory consumption
show processes memory | include EIGRP

# Monitor convergence times
show ip eigrp events

# Check interface utilization
show interfaces | include "rate"

# Monitor neighbor stability
show ip eigrp neighbors

# Track packet statistics
show ip eigrp traffic

Performance Best Practices

Performance Guidelines

  • Design for Performance: Implement hierarchical design with summarization
  • Monitor Continuously: Track performance metrics and trends
  • Optimize Selectively: Focus on critical paths and bottlenecks
  • Test Thoroughly: Validate performance improvements
  • Plan for Growth: Size infrastructure for future requirements
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