Network scripting automates repetitive configuration tasks, reduces human error, and enables consistent deployment across multiple devices. Scripts can range from simple command sequences to complex programs that interact with network APIs and management protocols.

Core Scripting Approaches

• CLI-based scripting - Automates command-line interface interactions using expect scripts, batch files, or shell scripts
• API-based scripting - Leverages REST APIs, NETCONF, or RESTCONF for programmatic device management
• Configuration templating - Uses templates with variables to generate device-specific configurations
• Event-driven automation - Triggers scripts based on network events, alarms, or monitoring thresholds

Common Scripting Languages and Tools

Python for Network Automation

• Most popular choice for network scripting due to extensive library ecosystem
• Netmiko library - Simplifies SSH connections to network devices (supports 100+ device types)
• Paramiko library - Lower-level SSH functionality for custom implementations
• Requests library - HTTP/HTTPS API interactions with network controllers
• NAPALM (Network Automation and Programmability Abstraction Layer with Multivendor support) - Provides unified API across different vendors

Ansible for Network Configuration

• Agentless architecture - No software installation required on target devices
• Playbooks - YAML-based configuration templates that define desired state
• Inventory files - Define groups of devices and their connection parameters
• Cisco modules - ios_command, ios_config, nxos_config for platform-specific tasks
• Idempotent operations - Running same playbook multiple times produces same result

Script Security Considerations

• Credential management - Use environment variables, key vaults, or encrypted files (never hardcode passwords)
• SSH key authentication - Preferred over password-based authentication for automated access
• Privilege escalation - Scripts should use least-privilege principle (enable secrets only when needed)
• Logging and auditing - Track all automated changes for compliance and troubleshooting
• Error handling - Include rollback mechanisms for failed configuration changes

Vocabulary

API (Application Programming Interface) - Standardized method for programs to interact with network devices or controllers

Idempotent - Property where running the same operation multiple times produces the same result

NETCONF - Network Configuration Protocol using XML over SSH for device management

RESTCONF - REST-based protocol providing HTTP interface to NETCONF datastores

Jinja2 - Templating engine commonly used with Python and Ansible for generating configurations

YAML - Human-readable data serialization standard used by Ansible playbooks

Practical Implementation Examples

• Backup automation - Daily configuration backups using show running-config via SSH
• VLAN deployment - Template-based VLAN creation across multiple switches
• Monitoring integration - Scripts that parse show command output and update monitoring systems
• Compliance checking - Automated verification that device configurations meet security standards
• Bulk configuration changes - Password updates, SNMP community changes, or NTP server modifications

Development Best Practices

• Test scripts in lab environment first - Never run untested automation against production
• Version control - Use Git or similar systems to track script changes and enable rollbacks
• Modular design - Create reusable functions for common tasks (connecting, parsing output, error handling)
• Configuration validation - Verify changes were applied correctly before moving to next device
• Parallel vs sequential execution - Balance speed with network stability (avoid overwhelming management plane)

Notes

• Start with simple read-only scripts (show commands) before attempting configuration changes
• Always include connection timeouts and retry logic - network devices can be slow to respond
• Cisco IOS has command history and rollback features - leverage archive and configuration replace for safer automation
• Python’s textfsm library excels at parsing structured data from CLI output (alternative to complex regex)
• Consider using configuration sessions on supported platforms - allows atomic commits and automatic rollbacks on errors
• SSH connection limits vary by platform - some devices support only 5-10 concurrent sessions
• Modern Cisco platforms support model-driven programmability with YANG models for more reliable automation than screen scraping