SSH and Paramiko

SSH (Secure Shell) is the primary protocol for accessing network device CLIs securely. Paramiko is a pure-Python implementation of SSHv2 that gives you programmatic control over SSH connections — the building block on which higher-level libraries like Netmiko are built.

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SSH Fundamentals

What is SSH?

SSH provides encrypted communication between a client and a server over an untrusted network:

Feature	Description
Encryption	All traffic is encrypted (AES, ChaCha20)
Authentication	Password or public-key based
Integrity	HMAC ensures data is not tampered with
Port	Default TCP port 22
Replaces	Telnet (port 23), which sends everything in cleartext

SSH Authentication Methods

Method	Description	Security
Password	User provides a username and password	Moderate — vulnerable to brute force
Public key	Client proves identity with a private key; server has the public key	Strong — no password transmitted
Keyboard-interactive	Server prompts for responses (e.g., MFA)	Strong — supports multi-factor

Key Exchange Process