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DHCP Troubleshooting

This guide addresses structured steps for troubleshooting DHCP issues with CE devices. The DHCP protocol automatically assigns IP addresses and any other network configurations to devices, reducing the complexity associated with network management. All devices may fail to connect to the network only after DHCP fails to work, thus causing connectivity. This document focuses on CE device DHCP verification and potential trouble areas.

Troubleshooting Steps​

Access the CE Terminal​

Log into the CE device and gain root access:

sudo su -

Verify DHCPv2 Configuration​

If the device implements DHCPv2, the actual settings can be examined.

cat /tmp/last_config_response.json | jq '.service.dhcpV2'

Example Response​

root@Backup_node:/tmp# cat /tmp/last_config_response.json | jq '.service.dhcpV2'
{
  "eth3": {
    "sharedNetworkName": "dhcpServer_eth3",
    "subnet": "172.10.2.0/24",
    "dnsServer": "172.10.2.1",
    "defaultRouter": "172.10.2.1",
    "dhcpRanges": [
      {
        "start": "172.10.2.51",
        "stop": "172.10.2.101"
      }
    ]
  }
}

This command will extract and display the last configuration response using DHCPv2 configuration. Especially useful in debugging situations that may not be related to specific DHCPv2 settings.

System Log Inspection​

Check the system log for any DHCP-related errors or warnings. The location and format of the system log varies on CE devices. Common commands include:

logread

Client Connectivity and IP Assignment Validation​

Check CE LAN Configuration and DHCP Status​

Ensure the CE device has a LAN IP address configured (e.g., 192.168.2.1) and the DHCP server is enabled.

On the CE interface:

  • Verify LAN IP under interface settings.
  • Check that DHCP is active and a valid IP range (e.g., 172.10.2.51 - 172.10.2.101) is configured.

Validate IP Assignment on Client Device​

After connecting the client to the CE LAN:

Run the following command on the client:​

ifconfig

Check the following:​

  • Interface name (i.e., eth0, wlan0) is up.
  • IP address is within the DHCP range configured on CE.
  • Subnet mask (i.e., 255.255.255.0) and gateway are correct.

Check Internet Connectivity from Client​

Run the ping test:​

ping 8.8.8.8

If the ping is successful, internet connectivity is working. If the ping fails, check:

  • The gateway IP should be verified on the CE to ensure it matches the expected network configuration. For example, if the assigned IP address is 192.168.10.5/24, then the gateway is typically 192.168.10.1. This gateway IP is usually the IP address of the modem or router. Check the subnet and gateway details in the CE device settings to confirm whether the gateway IP is correctly assigned and aligned with the router's IP.
  • The CE’s WAN or upstream internet connection.

Validate Traffic Policy with Speed Test​

If traffic shaping or bandwidth limits (i.e., 2 Mbps) are applied on the CE for DHCP clients:

Run speed test:​

speedtest

Analyze:​

  • Download/Upload speeds should match the policy (i.e., ~2 Mbps).
  • Large deviations may indicate issues in policy enforcement.