Day-06.md

Day 6: Advanced Topics - Error Handling and Custom YANG Paths

Concepts:

• Robust Error Handling: Implementing try-except blocks for network operations.
• Custom/Native YANG Paths: Working with vendor-specific YANG models and paths when OpenConfig is not sufficient or available. Arista's native paths are prefixed with eos_native:.
• Combining Operations: Performing multiple Get/Set operations in a single script.

Containerlab Setup (day6_lab.yaml):

name: day6_gnmi_lab
topology:
  nodes:
    ceos1:
      kind: arista_ceos
      image: ceos:4.34.0F
    ceos2:
      kind: arista_ceos
      image: ceos:4.34.0F
  links:
    - endpoints: ["ceos1:eth1", "ceos2:eth1"]

Deploy the lab:

sudo containerlab deploy --topo day6_gnmi_lab.yaml

Configure IPs on ceos1 and ceos2 for eth1 in CLI:

• ceos1 CLI:

  ssh admin@<ceos1-containername> # password: admin
  enable
  configure terminal
  interface Ethernet1
  no switchport
  ip address 10.0.0.1/30
  end
  

• ceos2 CLI:

  ssh admin@<ceos2-containername> # password: admin
  enable
  configure terminal
  interface Ethernet1
  no switchport
  ip address 10.0.0.2/30
  end
  

Code Examples:

1. day6_robust_config_and_status.py This script attempts to configure an IP on Ethernet2 on both ceos1 and ceos2, and then verifies their link status. It includes basic error handling.

from pygnmi.client import gNMIclient
import json

CEOS1_IP = "172.20.20.2" # **UPDATE THIS WITH YOUR CEOS1 IP**
CEOS2_IP = "172.20.20.3" # **UPDATE THIS WITH YOUR CEOS2 IP**
GNMI_PORT = 6030
USERNAME = "admin"
PASSWORD = "admin"

DEVICES = {
    "ceos1": CEOS1_IP,
    "ceos2": CEOS2_IP
}

def configure_interface_ip(gc, device_name, interface_name, ip_address, prefix_length):
    print(f"\n--- Configuring {interface_name} on {device_name} with {ip_address}/{prefix_length} ---")

    # To ensure the interface is a Layer 3 (routed) port, delete the 'switched-vlan' container.
    delete_switchport = [
        f"/interfaces/interface[name={interface_name}]/ethernet/switched-vlan"
    ]

    # Ensure the main interface is enabled
    enable_interface = [
        (
            f"/interfaces/interface[name={interface_name}]/config/enabled",
            True 
        )
    ]

    update_path_ip = [
        # 1. Enable IPv4 on the subinterface

            f"/interfaces/interface[name={interface_name}]/subinterfaces/subinterface[index=0]/openconfig-if-ip:ipv4/config",
            {"enabled": True} # Dict will be JSON-encoded by pygnmi
        ),
        # 2. Set IP address and prefix-length
        (
            f"/interfaces/interface[name={interface_name}]/subinterfaces/subinterface[index=0]/openconfig-if-ip:ipv4/addresses/address[ip={ip_address}]/config",
            {"ip": ip_address, "prefix-length": prefix_length} # Dict will be JSON-encoded by pygnmi
        )
    ]

    try:
        # 1. Delete the switched-vlan container (equivalent to 'no switchport')
        print(f"Attempting to delete switched-vlan config for {interface_name} on {device_name}...")
        response_delete_switchport = gc.set(delete=delete_switchport, encoding="json_ietf")
        print(f"Delete switchport response: {json.dumps(response_delete_switchport, indent=2)}")
        print(f"Successfully ensured {interface_name} is a routed port on {device_name}.")

        # 2. Ensure the main interface is enabled
        print(f"Attempting to enable {interface_name} on {device_name}...")
        response_enable_interface = gc.set(update=enable_interface, encoding="json_ietf")
        print(f"Enable interface response: {json.dumps(response_enable_interface, indent=2)}")
        print(f"Successfully enabled {interface_name} on {device_name}.")

        # 3. Configure the IP address and IPv4 enabled status
        print(f"Attempting to configure IP address {ip_address}/{prefix_length} on {interface_name}.")
        response_ip_config = gc.set(update=update_path_ip, encoding="json_ietf")
        print(f"IP configuration response: {json.dumps(response_ip_config, indent=2)}")
        print(f"Successfully configured IP on {interface_name} on {device_name}.")
        return True
    except Exception as e:
        print(f"Failed to configure {interface_name} on {device_name}: {e}")
        return False

def get_interface_oper_status(gc, device_name, interface_name):
    print(f"\n--- Getting operational status of {interface_name} on {device_name} ---")
    path = [f"/interfaces/interface[name={interface_name}]/state/oper-status"]
    try:
        result = gc.get(path=path, encoding="json_ietf", datatype="state")
        if result and 'notification' in result and result['notification']:
            for notification in result['notification']:
                if 'update' in notification:
                    for item in notification['update']:
                        if 'path' in item and 'val' in item:
                            status = item['val']
                            print(f"Operational status of {interface_name} on {device_name}: {status}")
                            return status
        print(f"Could not retrieve operational status for {interface_name} on {device_name}.")
        return None
    except Exception as e:
        print(f"Error getting operational status for {interface_name} on {device_name}: {e}")
        return None

if __name__ == "__main__":
    for device_name, ip_address in DEVICES.items():
        with gNMIclient(
            target=(ip_address, GNMI_PORT),
            username=USERNAME,
            password=PASSWORD,
            insecure=True
        ) as gc:
            ip_addr = f"172.16.0.{1 if device_name == 'ceos1' else 2}"
            configure_interface_ip(gc, device_name, "Ethernet2", ip_addr, 24)
            get_interface_oper_status(gc, device_name, "Ethernet1")

Challenge 6:

• Using an Arista native gNMI path (e.g., something under eos_native:/Smash/routing/status/route), try to retrieve the routing table of ceos1.
• Implement robust error handling in day6_robust_config_and_status.py to catch specific gRPC errors (e.g., grpc.RpcError) and provide more informative messages to the user.
• Extend day6_robust_config_and_status.py to also configure an OSPF process on both ceos1 and ceos2 using pygnmi and OpenConfig paths (if supported by cEOS for OSPF config via gNMI). Verify the OSPF neighbor state.