📘Cisco DevNet Associate (200-901 DEVASC)
1. Device-Level APIs: What They Are
Device-level APIs are ways to interact programmatically with network devices like routers and switches. Instead of logging into each device manually, you can use APIs to automate tasks, collect data, and change configurations.
For Cisco devices, there are mainly two families of device-level APIs:
a. RESTCONF
- RESTCONF is a RESTful API (uses HTTP methods like GET, POST, PATCH, DELETE) for network devices.
- It interacts with data modeled in YANG.
- Typical operations:
- GET → Read device configuration or operational data.
- POST/PUT → Add or change configurations.
- DELETE → Remove configurations.
- Example use in IT environment:
- A network engineer can query the status of all interfaces on a switch using a simple REST call instead of SSHing into each switch.
b. NETCONF
- NETCONF is a protocol for managing devices over SSH.
- It also uses YANG models.
- Key difference from RESTCONF: It’s stateful, which means it maintains a session and can handle transactions safely.
- Example use:
- Updating routing policies on multiple routers simultaneously while ensuring no conflicts.
c. gRPC / gNMI (primarily for NX-OS)
- NX-OS devices often support gRPC-based APIs like gNMI.
- gNMI is designed for streaming telemetry data, which is real-time info from devices.
- Example use:
- Monitoring CPU, memory, or interface statistics continuously for network analytics.
2. Dynamic Interfaces
Dynamic interfaces are virtual or temporary network interfaces created on-demand for a network device. They allow for flexible networking without physical changes.
a. IOS XE
- Supports dynamic interfaces like:
- Loopback interfaces → virtual interfaces mainly used for management or routing protocols.
- Tunnel interfaces → for VPNs or overlay networks (like VXLAN).
- Sub-interfaces → for VLAN tagging on physical ports.
- Why it matters:
- With APIs, these interfaces can be created, updated, or deleted dynamically.
- Example: A network automation script creates new VLAN interfaces for a data center deployment automatically.
b. NX-OS
- NX-OS also supports dynamic interfaces:
- Port channels (EtherChannel) → logical links combining multiple physical ports.
- SVI (Switched Virtual Interface) → for L3 routing on VLANs.
- Overlay interfaces → used in data center fabrics.
- Example: In a large data center, APIs can automatically spin up VXLAN tunnel interfaces for new tenant networks.
3. How Device-Level APIs & Dynamic Interfaces Work Together
- APIs let you configure and monitor dynamic interfaces without manual CLI work.
- Example IT workflow:
- A developer requests a new virtual network for a cloud application.
- A Python script calls RESTCONF on IOS XE switches to create VLANs and loopback interfaces.
- NX-OS leaf switches use gNMI telemetry to confirm interfaces are up.
- Network engineers get alerts automatically if something fails.
4. Key Exam Points
When preparing for 200-901 DEVASC, remember:
| Topic | Key Points for Exam |
|---|---|
| RESTCONF | Uses HTTP, YANG-modeled data, GET/POST/PUT/DELETE. |
| NETCONF | Uses SSH, stateful sessions, transactional config changes. |
| gNMI / gRPC | Primarily for NX-OS, streaming telemetry, modern data center automation. |
| Dynamic Interfaces (IOS XE) | Loopbacks, tunnels, sub-interfaces; can be scripted with APIs. |
| Dynamic Interfaces (NX-OS) | Port-channels, SVIs, overlay tunnels; programmable with APIs. |
| Integration | APIs + dynamic interfaces enable automated provisioning, monitoring, and scaling. |
5. Simple IT Example
- Scenario: A cloud service needs a new network segment.
- Manual way: Engineers log in to 10 switches, create VLANs, configure interfaces. Time-consuming and error-prone.
- Automated way using APIs:
- A Python script calls RESTCONF on IOS XE devices → creates VLANs, sub-interfaces.
- NX-OS gNMI telemetry confirms interfaces are operational.
- Entire network segment is ready in minutes.
- Exam tip: Focus on how APIs save time, reduce errors, and enable dynamic changes.
6. Exam Tip: Remember the Patterns
- IOS XE = more traditional network automation using RESTCONF/NETCONF.
- NX-OS = more data center-oriented with gNMI telemetry + dynamic overlays.
- Dynamic interfaces = virtual network constructs you can create or remove using APIs.
✅ In short:
Device-level APIs let you talk to network devices programmatically, and dynamic interfaces let you create temporary or virtual interfaces on-demand. Together, they form the backbone of network automation for both IOS XE and NX-OS devices.
