[Day #91 PyATS Series] Multi-Vendor VXLAN Overlay Health Validation Using pyATS for Cisco [Python for Network Engineer]

Introduction: Key Points

Welcome to Day #91 of our 101 Days of pyATS series, where we focus on automating advanced network validations using Python for Network Engineer workflows. Today’s Article dives deep into multi-vendor VXLAN overlay health validation using pyATS, targeting environments that rely on VXLAN for scalable Layer 2 overlay solutions.

VXLAN overlays are critical in modern data center fabric architectures, enabling network virtualization across physical boundaries. Ensuring consistent health of these overlays across multi-vendor devices (Cisco Nexus, Arista, Juniper, etc.) is essential for predictable service delivery.

In this comprehensive Article, we will:

• Automate health checks for VXLAN Tunnel Endpoints (VTEPs), ARP tables, BGP EVPN routes, and control plane connectivity.
• Validate both control plane and data plane consistency across multi-vendor deployments.
• Leverage structured pyATS test scripts to standardize and report results.
• Use both CLI and GUI-based methods to validate findings.

Let’s build a production-ready, automated validation framework that integrates into your day-to-day operations.

2. Topology Overview

My test environment simulates a multi-vendor VXLAN overlay fabric with the following components:

• Cisco Nexus 9000 Series (NX-OS) VTEPs: Acts as overlay gateways.
• Arista EOS Devices: Supporting VXLAN with EVPN.
• Juniper vQFX Devices: Also participating in VXLAN EVPN overlays.
• Underlay IP Fabric: Simple IP routing connecting devices (BGP, OSPF).
• Management Workstation: Runs the pyATS automation scripts and communicates with devices over SSH/API.

The topology diagram looks like this:

Topology & Communications

• Underlay Routing: OSPF/BGP connects all devices for basic IP connectivity.
• VXLAN Overlay: All VTEPs configured to advertise VXLAN Tunnel Endpoints using EVPN.
• pyATS Communication:
  • Uses SSH for CLI-based interaction.
  • Uses REST API for devices supporting API access (where applicable).
• Testbed Access:
  Defined via testbed.yml where IP addresses, credentials, and device roles are declared.

Workflow Script

from pyats.topology import loader
from genie.libs.parser.utils import get_parser_exclude_lines
from genie.libs.sdk.apis.iosxe.interface import verify_interface_status
from ats import aetest

class VXLANHealthCheck(aetest.Testcase):

    @aetest.setup
    def setup(self, testbed):
        self.testbed = testbed
        self.devices = self.testbed.devices
        for dev in self.devices.values():
            dev.connect()

    @aetest.test
    def vxlan_tunnel_status(self):
        for device in self.devices.values():
            output = device.parse('show nve peers')
            assert 'up' in output['nve_peer']['status'], \
                f"VXLAN peer not UP on {device.name}"

    @aetest.test
    def evpn_route_validation(self):
        for device in self.devices.values():
            output = device.parse('show bgp evpn route')
            assert output['vrf']['default']['routes'], \
                f"No EVPN routes found on {device.name}"

    @aetest.test
    def arp_table_check(self):
        for device in self.devices.values():
            output = device.parse('show ip arp')
            assert len(output['interfaces']) > 0, \
                f"Empty ARP table on {device.name}"

    @aetest.cleanup
    def cleanup(self):
        for device in self.devices.values():
            device.disconnect()

Explanation by Line

• Setup Phase:
  • Load testbed configuration.
  • Establish SSH/API connections to all devices.
• VXLAN Tunnel Status Test:
  • Parses show nve peers to confirm VXLAN peer status is UP.
  • Fails the test if any peer is not active.
• EVPN Route Validation:
  • Runs show bgp evpn route.
  • Checks that routes are populated for validation of control plane.
• ARP Table Check:
  • Uses show ip arp or vendor equivalent.
  • Ensures ARP entries exist for data-plane forwarding validation.
• Cleanup Phase:
  • Disconnect all device sessions cleanly.

testbed.yml Example

testbed:
  name: vxlan_validation
  devices:
    nexus1:
      os: nxos
      type: switch
      credentials:
        default:
          username: admin
          password: Cisco123!
      connections:
        cli:
          protocol: ssh
          ip: 192.168.1.10

    arista1:
      os: eos
      type: switch
      credentials:
        default:
          username: admin
          password: Arista123!
      connections:
        cli:
          protocol: ssh
          ip: 192.168.1.20

    juniper1:
      os: junos
      type: router
      credentials:
        default:
          username: admin
          password: Juniper123!
      connections:
        cli:
          protocol: ssh
          ip: 192.168.1.30

Post-validation CLI (Real Expected Output)

Example expected CLI output for a healthy VXLAN overlay:

nexus1# show nve peers
Peer IP          State
192.168.1.20    up
192.168.1.30    up

arista1# show bgp evpn route
Route Distinguisher : 100:1
Route Type : MAC/IP Advertisement
Next Hop : 192.168.1.10

juniper1> show arp
Interface          IP Address     MAC Address
ge-0/0/1          10.1.1.1       aa:bb:cc:dd:ee:ff

FAQs

Q1. Why should we automate VXLAN overlay health checks?
A1. Manual health checks are error-prone and time-consuming. Automation ensures consistency, reduces human error, speeds up troubleshooting, and integrates into CI/CD pipelines for continuous monitoring.

Q2. How does pyATS handle vendor differences in CLI commands?
A2. pyATS provides vendor-specific parsers, enabling consistent data structure extraction regardless of syntax differences across Cisco, Arista, or Juniper devices. This abstraction enables seamless multi-vendor automation.

Q3. Can pyATS detect VXLAN control plane and data plane mismatches?
A3. Yes. By validating EVPN routes (control plane) and ARP tables (data plane), pyATS detects discrepancies such as missing routes or unreachable endpoints, offering a comprehensive health snapshot.

Q4. What happens if a VXLAN peer is down during validation?
A4. The test fails with a clear message specifying the affected peer and device. Reports are generated in JSON or HTML format for easy audit and root-cause analysis.

Q5. Can this validation framework run in scheduled jobs?
A5. Absolutely. Using tools like Jenkins, GitHub Actions, or cron jobs, this pyATS framework can execute regularly and push reports to a central dashboard or email alerts.

Q6. How does this framework integrate with version control (GitOps)?
A6. Configuration and test scripts can be stored in GitHub. Changes are version-controlled, allowing pull requests, code reviews, and automated validation whenever a change is merged.

Q7. Is it possible to extend this framework for more advanced health checks?
A7. Yes. Additional checks like MAC address consistency, BUM (Broadcast/Unknown/Multicast) replication, and underlay latency checks can be implemented easily by adding more tests in the same structured framework.

YouTube Link

Watch the Complete Python for Network Engineer: Multi-Vendor VXLAN Overlay Health Validation Using pyATS for Cisco [Python for Network Engineer] Lab Demo & Explanation on our channel:

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