Ethernet Interface Guide - Link, DHCP & VLAN
Link up/down events, DHCP acquisition, VLAN tagging, speed negotiation, and cable fault simulation - what embedded Ethernet interface testing covers.
WHAT IS ETHERNET INTERFACE TESTING?
Ethernet interface testing is the validation of a device's physical Ethernet port behaviour - verifying that the device correctly handles link up/down events, negotiates speed and duplex, acquires IP addresses via DHCP or static configuration, and correctly handles VLAN tagging and network fault conditions.
Most embedded devices with an Ethernet port implement a TCP/IP stack and assume the Ethernet link works correctly. But the Ethernet interface itself - the PHY, the MAC, and the driver's handling of link state changes - is rarely tested systematically. Field failures from incorrect link-down handling, DHCP timeouts, wrong speed negotiation, and VLAN misconfiguration are common and preventable.
TestBot's approach: The Ethernet Interface Agent uses an Embien-built Raspberry Pi jig connected directly to the device's Ethernet port. The RPi acts as an active Ethernet endpoint - it can bring the link up and down, force specific speed and duplex modes, run a DHCP server, set VLAN tags, and ping the device. All of this is controlled programmatically from TestBot test blocks.
What the Ethernet Interface Agent Can Control and Measure
Each test block maps to a physical Ethernet interface behaviour that must be validated.
| Block | Function | What It Tests |
|---|---|---|
| ETH Link Up | Bring Ethernet link up on RPi port | Device detects link-up, driver initialises, link LED activates |
| ETH Link Down | Drop Ethernet link | Device detects link-down within 1s, enters correct failover or retry state |
| ETH Set Speed | Force 10/100/1000 Mbit/s | Device auto-negotiates to forced speed; mismatched speed detected |
| ETH Set Duplex | Force half/full duplex | Device negotiates to forced duplex; half-duplex collision handling validated |
| ETH Get Link Status | Read link state, speed, duplex | Confirms device reports correct link state to application layer |
| ETH DHCP Server Start | Start DHCP server on RPi port | Device sends DHCP Discover within 5s; IP lease assigned; device uses assigned IP |
| ETH DHCP Server Stop | Stop DHCP; simulate unavailability | Device handles DHCP timeout; retries; enters fallback (APIPA or static) |
| ETH Get DHCP Lease | Retrieve IP address leased to DUT | Confirms device accepted correct IP, subnet mask, and gateway |
| ETH Set Static IP | Configure RPi for static IP test | Device uses configured static IP; no DHCP traffic on static-configured devices |
| ETH Ping | Ping device from RPi | Confirms IP stack is active; round-trip time within spec |
| ETH Set VLAN | Configure VLAN tagging on RPi port | Device correctly handles tagged frames; untagged frames on VLAN-configured port rejected |
| ETH Simulate Cable Fault | Rapid link toggle | Device handles intermittent link; reconnects within timeout; no crash or lock-up |
| ETH Get Interface Stats | Read packet counts, error rates | TX/RX packet counts increase correctly; error frame rate within acceptable threshold |
TESTBOT ETHERNET INTERFACE AGENT
Ethernet Interface Test Agent
TestBot's Ethernet Interface Agent controls link state, speed, DHCP, VLAN, and ping via an Embien-built RPi jig. Requires the Ethernet Interface Jig hardware.
Ethernet Interface Test Scenarios With TestBot
| Scenario | Agents Used | Validated Outcome |
|---|---|---|
| Cold Start IP Acquisition | Ethernet Interface Agent - DHCP server + ping | DHCP lease acquired within 5s of power-up; device responds to ping within 10s |
| Link Failover Validation | Ethernet Interface Agent - Link Down + monitor | Application detects link-down within 1s; reconnects within 30s after Link Up |
| Speed Negotiation Test | Ethernet Interface Agent - ETH Set Speed (10/100/1000) | Device auto-negotiates correctly to each forced speed; wrong speed detected and logged |
| VLAN Tagged Frame Handling | Ethernet Interface Agent - ETH Set VLAN (VLAN 10) | Device accepts tagged frames on configured VLAN; untagged frames correctly handled |
| DHCP Lease Renewal | Ethernet Interface Agent - DHCP server + lease expiry | Device sends DHCP Request before lease expires; renewal completes within 3 retries |
| Static IP Validation | Ethernet Interface Agent - static IP config | No DHCP traffic generated; device uses configured static IP; correct subnet routing |
| Cable Fault Simulation | Ethernet Interface Agent - ETH Simulate Cable Fault (5 toggles/min) | Device reconnects after each toggle; no crash, no memory leak, error rate below 0.1% |
Frequently Asked Questions - Ethernet Interface Testing
Ethernet interface testing is the validation of a device's physical Ethernet port - link up/down handling, speed and duplex negotiation, DHCP IP address acquisition, VLAN tagging, and network fault recovery. It is distinct from protocol testing (Modbus TCP, ProfiNet, etc.) which validates application-layer communication over Ethernet.
RELATED GUIDES
Modbus Testing Guide
Modbus TCP runs over Ethernet - physical interface validation complements Modbus application testing.
DoIP Testing Guide
DoIP also uses Ethernet - physical interface validation is the first step before DoIP testing.
Industrial Agents
Ethernet Interface, Modbus, ProfiNet, and BACnet agents with pricing.
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Ethernet Interface Agent controls link, DHCP, VLAN, and speed. RPi jig required. 14-day free trial.