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[MX] JDHCPD is unaware of the current configuration and DHCP packets are dropped

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Article ID: KB34137 KB Last Updated: 22 May 2019Version: 2.0
Summary:

The JDHCPD process can be unaware of the present configuration. For example, the incoming DHCP messages can be considered as coming from an un-configured interface for DHCP exchange. Another example is when the configuration in the group (under 'system services dhcp-local-server group' or 'forwarding-options dhcp-relay group' or similar) cannot be applied, such as authentication of the incoming DHCP packets.

Symptoms:

In JDHCPD (DHCP client process)  logs, the following messages are seen:

Mar 26 09:30:00.769065 [MSTR][NOTE] [default:default][RLY][INET][demux0.1000] jdhcpd_packet_handle: BOOTPREQUEST demux0.1000 arrived on unconfigured interface DISCOVER, flags 3, config 0x0

The related DHCP packets are dropped.

This issue can also be seen when the configuration in the group (under 'system services dhcp-local-server group' or 'forwarding-options dhcp-relay group' or similar) cannot be applied, such as authentication of the incoming DHCP packets. In this case, the required parameters coming from RADIUS during authentication would not be present and the subscriber session cannot get established or establishes with incorrect parameters (like some default ones).

Cause:

The behavior was introduced  in Junos OS release 17.3R1 and 17.4R2 and present in 17.x (until 17.4R3), 18.x (until 18.1R4, 18.2R3, 18.3R3, 18.4R2, 18.2X75-D50 ) and 19.x (until 19.1R2, 19.2R1). Please contact JTAC to clarify if a particular release is affected by the described behavior. 

With the presence of the changes it is required to have at least one interface in the group knob (under 'system services dhcp-local-server group' or 'forwarding-options dhcp-relay group' or similar) before or during configuring other parameters in the group. In case no interfaces are present and the interfaces are added later, the previously configured parameters are not applied.

Solution:

It is important to have at least one interface in the group knob (under 'system services dhcp-local-server group' or 'forwarding-options dhcp-relay group' or similar) before or during configuring other parameters in the group.

If this requirement was not followed and the issue occurs, the workaround is to 'commit full' or restart JDHCPD ('restart dhcp-service').

Modification History:
2019-05-21: Added release information to the 'Cause' section of the article.
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