Netmiko SSH Automation

Use this skill when writing or reviewing Python automation that connects to network devices with Netmiko. Keep the default path read-only; config changes need a separate change window, peer review, and rollback plan.

When to Use

• Collecting show command output across routers, switches, or firewalls.
• Building a small audit script for interface, routing, or config evidence.
• Adding timeouts and exception handling to network SSH scripts.
• Parsing command output with TextFSM when a template exists.
• Reviewing automation before it touches production devices.

Safety Defaults

• Start with read-only send_command() collection.
• Keep inventory small and explicit; do not sweep whole address ranges.
• Use environment variables, a vault, or getpass; never hardcode credentials.
• Set connection and read timeouts.
• Limit concurrency so older devices are not overloaded.
• Require an explicit operator flag before send_config_set().
• Do not call save_config() until the change has been verified and approved.

Read-Only Connection Pattern

python
import os
from getpass import getpass
from netmiko import ConnectHandler
from netmiko.exceptions import (
    NetmikoAuthenticationException,
    NetmikoTimeoutException,
    ReadTimeout,
)

device = {
    "device_type": "cisco_ios",
    "host": "192.0.2.10",
    "username": os.environ.get("NETMIKO_USERNAME") or input("Username: "),
    "password": os.environ.get("NETMIKO_PASSWORD") or getpass("Password: "),
    "secret": os.environ.get("NETMIKO_ENABLE_SECRET"),
    "conn_timeout": 10,
    "auth_timeout": 20,
    "banner_timeout": 15,
    "read_timeout_override": 30,
}

try:
    with ConnectHandler(**device) as conn:
        if device.get("secret") and not conn.check_enable_mode():
            conn.enable()
        output = conn.send_command("show ip interface brief", read_timeout=30)
        print(output)
except NetmikoAuthenticationException:
    print("Authentication failed")
except NetmikoTimeoutException:
    print("SSH connection timed out")
except ReadTimeout:
    print("Command read timed out")

Use placeholder addresses from documentation ranges in examples. Keep real inventory in an ignored local file or a secrets-managed system.

Batch Collection

python
from concurrent.futures import ThreadPoolExecutor, as_completed
from typing import Any

def collect_show(device: dict[str, Any], command: str) -> dict[str, Any]:
    host = device["host"]
    try:
        with ConnectHandler(**device) as conn:
            output = conn.send_command(command, read_timeout=45)
        return {"host": host, "ok": True, "output": output}
    except (NetmikoAuthenticationException, NetmikoTimeoutException, ReadTimeout) as exc:
        return {"host": host, "ok": False, "error": type(exc).__name__}

results = []
with ThreadPoolExecutor(max_workers=8) as pool:
    futures = [pool.submit(collect_show, device, "show version") for device in devices]
    for future in as_completed(futures):
        results.append(future.result())

Keep max_workers low unless the device estate and AAA systems are known to handle higher connection volume.

Structured Parsing

Netmiko can ask TextFSM, TTP, or Genie to parse supported command output. Treat parser output as an optimization, not the only evidence path.

python
with ConnectHandler(**device) as conn:
    parsed = conn.send_command(
        "show ip interface brief",
        use_textfsm=True,
        raise_parsing_error=False,
        read_timeout=30,
    )

if isinstance(parsed, str):
    print("No parser template matched; store raw output for review")
else:
    for row in parsed:
        print(row)

If parsing drives a blocking decision, keep the raw command output alongside the parsed result so an operator can inspect mismatches.

Guarded Config Pattern

python
import os

commands = [
    "interface GigabitEthernet0/1",
    "description CHANGE-1234 UPLINK-TO-CORE",
]

apply_changes = os.environ.get("APPLY_NETWORK_CHANGES") == "1"

if not apply_changes:
    print("Dry run only. Candidate commands:")
    print("\n".join(commands))
else:
    with ConnectHandler(**device) as conn:
        conn.enable()
        before = conn.send_command("show running-config interface GigabitEthernet0/1")
        output = conn.send_config_set(commands)
        after = conn.send_command("show running-config interface GigabitEthernet0/1")
        print(before)
        print(output)
        print(after)
        print("Verify behavior before saving startup config.")

Saving the config is a separate approval step. In production, include a rollback snippet and capture before/after evidence in the change record.

Review Checklist

• Does the script identify an explicit inventory source?
• Are credentials absent from source, logs, and exception messages?
• Are conn_timeout, auth_timeout, and command read_timeout set?
• Are failures reported per device without stopping the whole batch?
• Does the script avoid broad scans and unbounded concurrency?
• Are config changes behind a dry-run or explicit operator flag?
• Is save_config() separate from the initial push and tied to verification?

Anti-Patterns

• Hardcoding passwords, enable secrets, or private keys in source.
• Sending config commands as the default code path.
• Running automation against a CIDR range instead of a reviewed inventory.
• Logging full running configs to shared systems without sanitization.
• Treating parser success as proof that the device state is correct.

See Also

• Skill: cisco-ios-patterns
• Skill: network-config-validation
• Skill: network-interface-health