NAPALM: vendor-neutral getters, config merge, replace and compare

What NAPALM is for

Every vendor has its own commands for the same question, such as "what are this device’s interfaces?". NAPALM (Network Automation and Programmability Abstraction Layer with Multivendor support) hides those differences behind one Python API. You pick a driver for the platform, and the same method names work everywhere. Under the hood each driver uses the best transport it can: SSH for IOS, eAPI for Arista EOS, NETCONF for Junos.

Getters: structured data without parsing

Getters are read-only methods that return dictionaries in a documented, vendor-neutral format. Examples include get_facts(), get_interfaces(), get_interfaces_ip(), get_arp_table(), get_lldp_neighbors() and get_bgp_neighbors(). Not every driver supports every getter, so check the support matrix in the NAPALM documentation.

import os
from napalm import get_network_driver

driver = get_network_driver("ios")
with driver(hostname="192.168.10.1",
            username=os.environ["NET_USER"],
            password=os.environ["NET_PASS"]) as device:
    facts = device.get_facts()
    print(facts["hostname"], facts["os_version"], facts["serial_number"])

    for name, intf in device.get_interfaces().items():
        if intf["is_enabled"] and not intf["is_up"]:
            print("Enabled but down:", name)

Because the output shape is the same for every vendor, one report script can audit a mixed network.

Merge, replace and compare

NAPALM changes configuration through a candidate. You load changes, inspect the difference, then commit or throw them away.

• Merge (load_merge_candidate): adds your lines to the running configuration, like typing them in. Good for small, additive changes.
• Replace (load_replace_candidate): makes the device match your file exactly, removing anything not in it. Powerful for enforcing a full intended configuration, and dangerous if the file is incomplete.

import os
from napalm import get_network_driver

driver = get_network_driver("eos")
with driver("192.168.10.2", os.environ["NET_USER"], os.environ["NET_PASS"]) as device:
    device.load_merge_candidate(filename="ntp_snippet.cfg")
    diff = device.compare_config()
    if not diff:
        print("Nothing to change")
        device.discard_config()
    else:
        print(diff)
        if input("Commit? [y/N] ").lower() == "y":
            device.commit_config()
        else:
            device.discard_config()

Tip: compare_config() with no commit is a safe, read-only way to detect drift: load the intended configuration as a replace candidate, print the difference, then discard.

Platform notes and good practice

• Test replace operations in a lab first; a missing management line in your file can cut off your own access.
• Keep intended configurations in Git so every change has history and review.
• Use rollback() after a commit if verification fails, and know how it behaves on your platform.
• Combine NAPALM with Nornir (the nornir_napalm plugin) or Ansible to run across many devices.