This article provides information on how to identify JDHCPD issues that are related to address assignment failure.

Starting with 12.x, the DHCP process has been modified and the new process is JDHCP. Even though both processes are running on the device, it is recommended to use JDHCP, not DHCP. As the configuration has changed, so has the troubleshooting process.

For JDHCP configuration, refer to:

• KB26898 - [SRX] JDHCP configuration in Ethernet switching [juniper.net]
• KB26899 - [SRX] Configuring JDHCP on a VLAN in a routing instance [juniper.net]
• KB34617 -[SRX] How to configure JDHCP server in a logical system [juniper.net]  

Background information:

DHCP is a client server communication, and to understand where and why it is breaking, it is recommended to look at both the client and server. It uses the 67(bootps) and 68(bootpc) UDP ports for communication.

• bootpc = bootp Client
• bootps = bootp Server

Pay attention to the Transaction ID, Server Identification bit, and time taken between each packet. It is also important to consider if the communication is using broadcast or unicast (verify the same in the bootp flag under the Bootstrap Protocol).

Troubleshooting flow:

Understand and isolate the issue. For example, the client is unable to obtain the IP address.

Issue isolation:

• Are all clients unable to obtain the IP address?
• Is the Windows PC unable to obtain the IP, MAC, IP Phone, LAN PC, or wireless address?
• Is any specific version unable to obtain the IP address? Is this a constant or intermittent issue?

Verify the connectivity:

• How are the clients connected? Over wireless or LAN?
• Is the directly connected PC able to obtain the IP address or not?
• Manually assign an IP address on the PC and try to ping the SRX device to verify the connectivity.

Required information:

• Flow traceoption with DHCP UDP port specified as  packet filters
• JDHCP traceoption.
• Packet captures or tcpdump in the pcap format from the SRX device.
• Packet captures on the client machine.

Flow debug:

set security flow traceoptions file DHCPTRACE
set security flow traceoptions file size 20m
set security flow traceoptions file files 5
set security flow traceoptions flag basic-datapath
set security flow traceoptions flag packet-drops
set security flow traceoptions packet-filter R1 source-port 68
set security flow traceoptions packet-filter R2 source-port 67

The logs will be created at /var/log/DHCPTRACE .

JDHCPD debug:

set system processes dhcp-service traceoptions file JDHCPDEBUG
set system processes dhcp-service traceoptions file size 20m
set system processes dhcp-service traceoptions file files 5
set system processes dhcp-service traceoptions flag all

The logs will be created at /var/log/JDHCPDEBUG .

Note: The configured traceoptions could impact performance of the SRX. Deactivate or delete them after the needed information is obtained.

PCAP on the SRX interface:

For more information, refer to KB11709 - [SRX] How to Create a PCAP packet capture on a J-Series or SRX Branch device [juniper.net] .

2020-07-25: Added link to KB on DHCP in LSYS.