Technical Tip: Troubleshooting DHCP for isolation VLANs
Description
This article describes how to troubleshoot issues with Hosts in isolation that are not receiving an IP address.
Scope
FortiNAC.
Solution
Log in to the CLI of the Server/Application server and do the following:
- Ensure the appliance is fully booted.
- Control processes are running (Yams). Type:
jps
- DHCP service is running:
service dhcpd status
Example of running service:
service dhcpd status
Redirecting to /bin/systemctl status dhcpd.service
dhcpd.service - DHCPv4 Server Daemon
Loaded: loaded (/usr/lib/systemd/system/dhcpd.service; enabled; vendor preset: disabled)
Active: active (running) since Thu 2019-12-26 15:44:53 EST; 4 days ago
...
On FortiNAC-OS:
execute enter-shell
~$ systemctl status dhcpd
Example of running service:
execute enter-shell
~$ systemctl status dhcpd
dhcpd.service - DHCPv4 Server Daemon
Loaded: loaded (/lib/systemd/system/dhcpd.service; enabled; vendor preset: disabled)
Active: active (running) since Sat 2026-04-04 01:02:33 CEST; 6 days ago
- If the DHCP is not running:
Verify the eth1 interface is up. In the CLI of the Server or Application Server, run the command:
ip addr show dev eth1
Example:
ip addr show dev eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
...
- If eth1 is up, attempt restarting the service:
service dhcpd restart
- If the service fails to start and output reports Read-only file system, refer to the related KB article: Technical Note: Drive in Read Only mode.
- If eth1 is administratively up but has no link, troubleshoot the network connection. See the related KB article: Technical Tip: DHCP service not running after a power event.
- Ensure there is ample disk space on the file system.
df -h
- If DHCPD is running, refer to the related KB articles below for additional troubleshooting steps:
- If additional information is needed to determine the problem, collect logs. Refer to the following KB article: Technical Tip: How to get a debug log report from FortiNAC-CA or FortiNAC-Manager.
- Review the following logs for errors:
/bsc/logs/messages
/bsc/logs/dhcpd.log
/bsc/logs/dhcpd.log