How to Check whether dhcp-server exists for that subnet before creating a subnet

Question

I am stuck with a neutron issue.

I have two nodes namely controller and compute neutron component is installed in controller node. Restarted DHCP, L3 Agent services.

1. we are using namespaces for dhcp agent.
2. Created a private network by specifying provider network type as flat. After that before creating subnet we want to check if dhcp-server exists for that subnet.

our subnet is 10.88.210.0/24

Answer 1

Try dhcp-discover

Sends a DHCPINFORM request to a host on UDP port 67 to obtain all the local configuration parameters without allocating a new address.

DHCPINFORM is a DHCP request that returns useful information from a DHCP server, without allocating an IP address. 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.

Example Usage

nmap -sU -p 67 --script=dhcp-discover <target>

Output

Interesting ports on 192.168.1.1:
PORT   STATE SERVICE
67/udp open  dhcps
| dhcp-discover:
|   DHCP Message Type: DHCPACK
|   Server Identifier: 192.168.1.1
|   IP Address Lease Time: 1 day, 0:00:00
|   Subnet Mask: 255.255.255.0
|   Router: 192.168.1.1
|_  Domain Name Server: 208.81.7.10, 208.81.7.14

Loop through the hosts in your subnet until you find dhcp server.

Reference