---
title: "dhcpd: send_packet: Invalid argument"
slug: "aa-01443"
description: "This error indicates either a resource problem or a wrong error code from the operating system kernel."
tags: ["isc dhcp"]
updated: 2018-10-30T19:50:53Z
published: 2018-10-30T19:50:54Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://kb.isc.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Why is my server logging: "dhcpd: send_packet: Invalid argument"?

```
dhcpd: send_packet: Invalid argument
dhcpd: dhcp.c:3730: Failed to send 300 byte long packet over fallback interface.
```

This error message is seen due to two different problems:

1. The server has a resource problem - specifically that the ARP cache (sometimes known as 'Neighbour table') is full.
2. The wrong error code (EINVAL instead of ENOBUFS) is being returned by the operating system kernel in some circumstances. This error message was seen from Linux kernel 3.16, but the correct error was logged by Linux kernel 3.2.

The correct message would have reported "No buffer space available" instead of "Invalid argument."

Another message that might also be seen in newer versions of Linux (3.2 and above) in `kern.log` is:

```
ipv4: Neighbour table overflow.
```

Increasing the ARP cache can be achieved by adjusting the `gc_thresh2` and `gc_thresh3` Linux kernel settings.