Nmap NSE net: dhcp-discover

Sends a DHCPDISCOVER request to a host on UDP port 67. The response comes back to UDP port 68, and is read using pcap (due to the inability for a script to choose its source port at the moment). DHCPDISCOVER is a DHCP request that returns useful information from a DHCP server. The request sends a list of which fields it wants to know (a handful by default, every field if verbosity is turned on), and the server responds with the fields that were requested. It should be noted that the server doesn't have to return every field, nor does it have to return them in the same order, or honour the request at all. A Linksys WRT54g, for example, completely ignores the list of requested fields and returns a few standard ones. This script displays every field it receives. With script arguments, the type of DHCP request can be changed, which can lead to interesting results. Additionally, the MAC address can be randomized, which should override the cache on the DHCP server and assign a new IP address. Extra requests can also be sent to exhaust the IP address range more quickly. DHCPINFORM is another type of DHCP request that requests the same information, but doesn't reserve an address. Unfortunately, because many home routers simply ignore DHCPINFORM requests, we opted to use DHCPDISCOVER instead. Some of the more useful fields: * DHCP Server (the address of the server that responded) * Subnet Mask * Router * DNS Servers * Hostname SYNTAX: fake_requests: Set to an integer to make that many fake requests before the real one(s). This could be useful, for example, if you also use 'randomize_mac' and you want to try exhausting all addresses. requests: Set to an integer to make up to that many requests (and display the results). randomize_mac: Set to 'true' or '1' to send a random MAC address with the request (keep in mind that you may not see the response). This should cause the router to reserve a new IP address each time. dhcptype: The type of DHCP request to make. By default, DHCPDISCOVER is sent, but this argument can change it to DHCPOFFER, DHCPREQUEST, DHCPDECLINE, DHCPACK, DHCPNAK, DHCPRELEASE or DHCPINFORM. Not all types will evoke a response from all servers, and many require different fields to contain specific values.