# DHCP

When connecting a computer to most enterprise networks, if the Dynamic Host Configuration Protocol (DHCP) is enabled, it will assign an IP address to that computer, and send a lot of information. Nameservers and domain names are usually set through DHCP offer packets.

On UNIX-like systems, the `/etc/resolv.conf` file will store information for name resolution operations after the DHCP offer.

The [nmap](https://nmap.org/) tool can be used with its [broadcast-dhcp-discover.nse](https://nmap.org/nsedoc/scripts/broadcast-dhcp-discover.html) script to easily parse those packets.

```bash
nmap --script broadcast-dhcp-discover
```

{% hint style="info" %}
In many cases, there will be MAC address filtering, static IP addressing, VLANs or other [NAC (Network Access Control) and 802.1x](https://github.com/v4resk/red-book/blob/main/physical/networking/network-access-control.md) that can prevent testers from obtaining this information. In those situations, [Wireshark](https://www.wireshark.org/) can be used to manually inspect broadcast and multicast packets that travel on the network and find valuable information that could help bypass those mitigations.
{% endhint %}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://red.infiltr8.io/ad/recon/network/dhcp.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.