Chapter 11: Static and Dynamic Routing

Learning Objectives

By the end of this chapter, you will be able to: - Configure and troubleshoot static routing - Understand routing table concepts and administrative distance - Implement default routes and route summarization - Compare static and dynamic routing approaches - Design routing solutions for different network scenarios

Routing Fundamentals

What is Routing?

Routing is the process of selecting paths in a network along which to send network traffic. Routers use routing tables to determine the best path to forward packets toward their destination.

Key Routing Concepts

• Routing Table: Database containing network destinations and next-hop information
• Administrative Distance: Trustworthiness rating of routing information sources
• Metric: Value used to determine the best path when multiple routes exist
• Next Hop: The next router in the path toward the destination
• Route Summarization: Combining multiple routes into a single advertisement

Routing Table Structure

# Example routing table output
Router# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       + - replicated route, % - next hop override

Gateway of last resort is 192.168.1.1 to network 0.0.0.0

S*    0.0.0.0/0 [1/0] via 192.168.1.1
      10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
C        10.1.1.0/24 is directly connected, GigabitEthernet0/0/0
L        10.1.1.1/32 is directly connected, GigabitEthernet0/0/0
S        10.2.2.0/24 [1/0] via 10.1.1.2
S        10.3.3.0/24 [1/0] via 10.1.1.3

Static Routing

Static Route Configuration

Static routes are manually configured routes that don’t change unless manually modified.

Basic Static Route Lab

# Static routing lab topology
name: static-routing-lab
prefix: static

topology:
  nodes:
    r1:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.10
      startup-config: |
        hostname Router1
        !
        interface GigabitEthernet0/0/0
         ip address 10.1.1.1 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/1
         ip address 192.168.1.1 255.255.255.0
         no shutdown
        !

    r2:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.11
      startup-config: |
        hostname Router2
        !
        interface GigabitEthernet0/0/0
         ip address 10.1.1.2 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/1
         ip address 192.168.2.1 255.255.255.0
         no shutdown
        !

    r3:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.12
      startup-config: |
        hostname Router3
        !
        interface GigabitEthernet0/0/0
         ip address 10.1.1.3 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/1
         ip address 192.168.3.1 255.255.255.0
         no shutdown
        !

    pc1:
      kind: linux
      image: alpine:latest
      mgmt-ipv4: 172.20.20.21
      exec:
        - ip addr add 192.168.1.10/24 dev eth1
        - ip route add default via 192.168.1.1

    pc2:
      kind: linux
      image: alpine:latest
      mgmt-ipv4: 172.20.20.22
      exec:
        - ip addr add 192.168.2.10/24 dev eth1
        - ip route add default via 192.168.2.1

    pc3:
      kind: linux
      image: alpine:latest
      mgmt-ipv4: 172.20.20.23
      exec:
        - ip addr add 192.168.3.10/24 dev eth1
        - ip route add default via 192.168.3.1

  links:
    # Router interconnections
    - endpoints: ["r1:eth1", "r2:eth1"]
    - endpoints: ["r1:eth1", "r3:eth1"]  # Multi-access network

    # PC connections
    - endpoints: ["r1:eth2", "pc1:eth1"]
    - endpoints: ["r2:eth2", "pc2:eth1"]
    - endpoints: ["r3:eth2", "pc3:eth1"]

Configuring Static Routes

# Deploy the lab
containerlab deploy -t static-routing-lab.yml

# Connect to Router1 and configure static routes
docker exec -it clab-static-r1 cli

# Configure static routes on R1
configure terminal
ip route 192.168.2.0 255.255.255.0 10.1.1.2
ip route 192.168.3.0 255.255.255.0 10.1.1.3
exit

# Verify routing table
show ip route

# Test connectivity
ping 192.168.2.10
ping 192.168.3.10

Static Route Types

Standard Static Routes

# Basic static route syntax
ip route <destination_network> <subnet_mask> <next_hop_ip>

# Examples
ip route 192.168.2.0 255.255.255.0 10.1.1.2
ip route 10.0.0.0 255.0.0.0 172.16.1.1

Default Routes

# Default route (gateway of last resort)
ip route 0.0.0.0 0.0.0.0 <next_hop_ip>

# Example
ip route 0.0.0.0 0.0.0.0 192.168.1.1

Floating Static Routes

Backup routes with higher administrative distance:

# Primary route (AD = 1)
ip route 192.168.2.0 255.255.255.0 10.1.1.2

# Backup route (AD = 5)
ip route 192.168.2.0 255.255.255.0 10.1.1.3 5

Interface-Based Static Routes

# Route pointing to an interface (for point-to-point links)
ip route 192.168.2.0 255.255.255.0 Serial0/0/0

# Fully specified route (interface + next-hop)
ip route 192.168.2.0 255.255.255.0 Serial0/0/0 10.1.1.2

Advanced Static Routing Lab

# Advanced static routing with redundancy
name: advanced-static-routing
prefix: adv-static

topology:
  nodes:
    # Core routers
    core-r1:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.10
      startup-config: |
        hostname Core-Router-1
        !
        interface GigabitEthernet0/0/0
         description To-Core-R2-Primary
         ip address 10.1.1.1 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description To-Core-R2-Backup
         ip address 10.1.2.1 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/2
         description To-Branch-R1
         ip address 10.2.1.1 255.255.255.252
         no shutdown
        !
        interface Loopback0
         ip address 1.1.1.1 255.255.255.255
        !
        ! Static routes with redundancy
        ip route 2.2.2.2 255.255.255.255 10.1.1.2
        ip route 2.2.2.2 255.255.255.255 10.1.2.2 5
        ip route 192.168.10.0 255.255.255.0 10.2.1.2
        ip route 0.0.0.0 0.0.0.0 10.1.1.2
        ip route 0.0.0.0 0.0.0.0 10.1.2.2 5
        !

    core-r2:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.11
      startup-config: |
        hostname Core-Router-2
        !
        interface GigabitEthernet0/0/0
         description To-Core-R1-Primary
         ip address 10.1.1.2 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description To-Core-R1-Backup
         ip address 10.1.2.2 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/2
         description To-Internet
         ip address 203.0.113.1 255.255.255.252
         no shutdown
        !
        interface Loopback0
         ip address 2.2.2.2 255.255.255.255
        !
        ! Static routes
        ip route 1.1.1.1 255.255.255.255 10.1.1.1
        ip route 1.1.1.1 255.255.255.255 10.1.2.1 5
        ip route 192.168.10.0 255.255.255.0 10.1.1.1
        ip route 192.168.10.0 255.255.255.0 10.1.2.1 5
        ip route 0.0.0.0 0.0.0.0 203.0.113.2
        !

    branch-r1:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      mgmt-ipv4: 172.20.20.12
      startup-config: |
        hostname Branch-Router-1
        !
        interface GigabitEthernet0/0/0
         description To-Core-R1
         ip address 10.2.1.2 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description LAN-Interface
         ip address 192.168.10.1 255.255.255.0
         no shutdown
        !
        ! Static routes
        ip route 0.0.0.0 0.0.0.0 10.2.1.1
        !

    internet-sim:
      kind: linux
      image: alpine:latest
      mgmt-ipv4: 172.20.20.100
      exec:
        - ip addr add 203.0.113.2/30 dev eth1
        - ip route add 0.0.0.0/0 via 203.0.113.1

    branch-pc:
      kind: linux
      image: alpine:latest
      mgmt-ipv4: 172.20.20.20
      exec:
        - ip addr add 192.168.10.10/24 dev eth1
        - ip route add default via 192.168.10.1

  links:
    # Core router connections (redundant)
    - endpoints: ["core-r1:eth1", "core-r2:eth1"]
    - endpoints: ["core-r1:eth2", "core-r2:eth2"]

    # Branch connection
    - endpoints: ["core-r1:eth3", "branch-r1:eth1"]

    # Internet connection
    - endpoints: ["core-r2:eth3", "internet-sim:eth1"]

    # Branch LAN
    - endpoints: ["branch-r1:eth2", "branch-pc:eth1"]

Administrative Distance

Administrative Distance (AD) determines the trustworthiness of routing information sources. Lower AD values are preferred.

Default Administrative Distances

Route Source	Administrative Distance
Connected Interface	0
Static Route	1
EIGRP	90
OSPF	110
RIP	120
External EIGRP	170
Unknown	255 (unreachable)

Configuring Administrative Distance

# Static route with custom AD
ip route 192.168.1.0 255.255.255.0 10.1.1.2 150

# Modify AD for routing protocols
router ospf 1
 distance 95

router eigrp 100
 distance eigrp 85 155

Route Summarization

Route summarization reduces routing table size by combining multiple routes into a single advertisement.

Manual Route Summarization

# Instead of advertising individual subnets:
# 192.168.1.0/24
# 192.168.2.0/24
# 192.168.3.0/24
# 192.168.4.0/24

# Advertise summary route:
ip route 192.168.0.0 255.255.252.0 10.1.1.2

Summarization Lab Example

# Route summarization lab
name: route-summarization
topology:
  nodes:
    hub-router:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      startup-config: |
        hostname Hub-Router
        !
        interface GigabitEthernet0/0/0
         ip address 10.1.1.1 255.255.255.0
         no shutdown
        !
        ! Summary route instead of individual routes
        ip route 192.168.0.0 255.255.252.0 10.1.1.2
        !

    spoke-router:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      startup-config: |
        hostname Spoke-Router
        !
        interface GigabitEthernet0/0/0
         ip address 10.1.1.2 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/1
         ip address 192.168.1.1 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/2
         ip address 192.168.2.1 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/3
         ip address 192.168.3.1 255.255.255.0
         no shutdown
        !
        ! Individual routes back to hub
        ip route 0.0.0.0 0.0.0.0 10.1.1.1
        !

  links:
    - endpoints: ["hub-router:eth1", "spoke-router:eth1"]

Dynamic Routing Overview

Dynamic routing protocols automatically discover and maintain routing information.

Types of Dynamic Routing Protocols

Distance Vector Protocols

• RIP (Routing Information Protocol)
• EIGRP (Enhanced Interior Gateway Routing Protocol)

Characteristics: - Share routing tables with neighbors - Use hop count or composite metrics - Prone to routing loops - Slower convergence

Link State Protocols

• OSPF (Open Shortest Path First)
• IS-IS (Intermediate System to Intermediate System)

Characteristics: - Share link state information - Build topology database - Use SPF algorithm - Faster convergence - More CPU and memory intensive

Comparison: Static vs Dynamic Routing

Aspect	Static Routing	Dynamic Routing
Configuration	Manual	Automatic
Scalability	Poor	Good
Convergence	None	Fast
Resource Usage	Low	Higher
Security	High	Medium
Maintenance	High	Low
Flexibility	Low	High

When to Use Static Routing

1. Small networks with few routers
2. Stub networks with single exit point
3. Security-critical environments
4. Bandwidth-constrained links
5. Default routes to ISPs

When to Use Dynamic Routing

1. Large networks with many routers
2. Redundant paths requiring automatic failover
3. Frequently changing topologies
4. Load balancing requirements
5. Complex network designs

Routing Troubleshooting

Common Routing Issues

Missing Routes

# Symptoms
ping fails to remote networks
traceroute shows incomplete path

# Diagnosis
show ip route
show ip route <destination>

# Resolution
Add missing static routes
Verify next-hop reachability

Routing Loops

# Symptoms
High CPU utilization
Packets with decreasing TTL
Intermittent connectivity

# Diagnosis
traceroute shows repeating hops
show ip route shows conflicting routes

# Resolution
Verify route summarization
Check administrative distances
Implement route filtering

Suboptimal Routing

# Symptoms
Poor performance
Unexpected path selection

# Diagnosis
show ip route
traceroute analysis
show ip route <destination> longer-prefixes

# Resolution
Adjust administrative distances
Modify route metrics
Implement policy routing

Diagnostic Commands

Essential Routing Commands

# Routing table
show ip route
show ip route summary
show ip route <network>

# Interface status
show ip interface brief
show interfaces

# Connectivity testing
ping <destination>
traceroute <destination>
telnet <destination> <port>

# Route verification
show ip route <destination> longer-prefixes
show ip cef <destination>

Advanced Troubleshooting

# Debug routing (use carefully)
debug ip routing
debug ip packet

# Route monitoring
show ip route summary
show ip route profile

# Interface statistics
show interfaces <interface> | include (input|output) rate
show interfaces <interface> counters

Practical Routing Scenarios

Scenario 1: Hub-and-Spoke with Backup

# Hub-and-spoke with backup connectivity
name: hub-spoke-backup
topology:
  nodes:
    hub:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      startup-config: |
        hostname Hub
        !
        interface GigabitEthernet0/0/0
         description Primary-to-Spoke1
         ip address 10.1.1.1 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description Primary-to-Spoke2
         ip address 10.1.2.1 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/2
         description Backup-Link
         ip address 10.1.3.1 255.255.255.252
         no shutdown
        !
        ! Primary routes
        ip route 192.168.1.0 255.255.255.0 10.1.1.2
        ip route 192.168.2.0 255.255.255.0 10.1.2.2
        ! Backup routes (higher AD)
        ip route 192.168.1.0 255.255.255.0 10.1.3.2 5
        ip route 192.168.2.0 255.255.255.0 10.1.3.2 5
        !

    spoke1:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      startup-config: |
        hostname Spoke1
        !
        interface GigabitEthernet0/0/0
         description Primary-to-Hub
         ip address 10.1.1.2 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description LAN
         ip address 192.168.1.1 255.255.255.0
         no shutdown
        !
        interface GigabitEthernet0/0/2
         description Backup-to-Spoke2
         ip address 10.1.3.2 255.255.255.252
         no shutdown
        !
        ! Default route via hub
        ip route 0.0.0.0 0.0.0.0 10.1.1.1
        ! Backup default route
        ip route 0.0.0.0 0.0.0.0 10.1.3.1 5
        !

    spoke2:
      kind: cisco_iosxe
      image: cisco/iosxe:latest
      startup-config: |
        hostname Spoke2
        !
        interface GigabitEthernet0/0/0
         description Primary-to-Hub
         ip address 10.1.2.2 255.255.255.252
         no shutdown
        !
        interface GigabitEthernet0/0/1
         description LAN
         ip address 192.168.2.1 255.255.255.0
         no shutdown
        !
        ! Default route via hub
        ip route 0.0.0.0 0.0.0.0 10.1.2.1
        !

  links:
    - endpoints: ["hub:eth1", "spoke1:eth1"]
    - endpoints: ["hub:eth2", "spoke2:eth1"]
    - endpoints: ["hub:eth3", "spoke1:eth3"]  # Backup link

Scenario 2: Load Balancing

# Equal-cost load balancing
startup-config: |
  ! Multiple equal-cost paths
  ip route 192.168.10.0 255.255.255.0 10.1.1.2
  ip route 192.168.10.0 255.255.255.0 10.1.2.2

  ! Enable load balancing
  maximum-paths 4

Best Practices

Static Routing Best Practices

1. Documentation: Maintain accurate network diagrams and route tables
2. Consistency: Use consistent naming and addressing schemes
3. Redundancy: Implement backup routes with appropriate AD
4. Summarization: Use route summarization to reduce table size
5. Security: Implement route filtering and access controls

Route Management

1. Change Control: Document all routing changes
2. Testing: Test routes in lab before production
3. Monitoring: Monitor routing table size and convergence
4. Backup: Maintain configuration backups
5. Automation: Use scripts for repetitive tasks

Performance Considerations

1. Route Table Size: Monitor and optimize table size
2. Convergence Time: Minimize convergence delays
3. CPU Usage: Monitor routing process CPU utilization
4. Memory Usage: Track routing table memory consumption
5. Bandwidth: Consider routing protocol overhead

Summary

Static and dynamic routing serve different purposes in network design. Static routing provides simplicity and security for small networks and specific use cases, while dynamic routing offers scalability and automatic adaptation for larger, more complex networks. Understanding both approaches and their appropriate applications is essential for effective network design.

Key concepts covered: - Static route configuration and types - Administrative distance and route selection - Route summarization techniques - Comparison of static vs dynamic routing - Troubleshooting methodologies - Practical implementation scenarios

In the next chapter, we’ll dive deep into OSPF, one of the most important dynamic routing protocols for enterprise networks.

Review Questions

1. What are the advantages and disadvantages of static routing?
2. How does administrative distance affect route selection?
3. When would you use floating static routes?
4. What are the benefits of route summarization?
5. How do you troubleshoot routing connectivity issues?

Hands-on Exercises

Exercise 1: Basic Static Routing

1. Deploy the static routing lab topology
2. Configure static routes on all routers
3. Test connectivity between all networks
4. Verify routing tables and trace packet paths

Exercise 2: Redundant Static Routes

1. Implement the advanced static routing lab
2. Configure primary and backup routes
3. Test failover by disabling primary links
4. Monitor route table changes during failover

Exercise 3: Route Summarization

1. Create a network with multiple subnets
2. Implement route summarization
3. Compare routing table sizes before and after
4. Test connectivity to verify summarization works

Exercise 4: Troubleshooting Scenarios

1. Create various routing problems (missing routes, loops)
2. Practice diagnostic commands and procedures
3. Develop systematic troubleshooting approaches
4. Document solutions and prevention strategies

Additional Resources

• Cisco Routing Configuration Guide
• Static Routing Best Practices
• Administrative Distance Reference
• Route Summarization Guide