Another system that is useful and still used in the cloud environment is DHCP.
The DHCP specifications would include the client/server protocol that
automatically provides an IP host with an IP address and other related
configuration information such as a subnet mask and default gateway, and it's
designed to assign IP address is from a pool of pre‑allocated addresses on a
DHCP server. Based upon the specification RFC 2131, the client transmits on port
67, and the server responds on ports 68.
The DHCP options would include things like DNS settings,
the domain names, and also Network Time Protocol servers. Here are
some major issues when it comes to DHCP security.
You could have rogue DHCP systems that are plugging into a secure
network and then becoming the source point for giving all the previous
configurations that we were talking about.
There's also no native encryption of traffic,
which means that there's no secrecy, which is another way the
attacker could be surveilling the environment.
There could also be interception and manipulation of the traffic so
that you're passing the traffic, but you're changing it as it's
going through some intermediary system.
The DHCP process looks like this.
You have a DHCP client, and you have a DHCP server.
The client sends out a broadcast with a DHCP discover packet, and the
server responds with a DHCP offer, giving the client an available address
to use. The client responds back with a DHCP request to use the offered
address, and then the server responds back to the client with an
acknowledgement that allows that client to bind the requested address to
the network interface card.
When we think about the halfway process through a lease,
what the client does is sends the same address at step three of
the request to the server, and the server responds back with an
acknowledgement typically that says yes,
you can still use that address.
The automatic private IP addressing can be helpful when doing
local configuration options or local backups.
There is a situation recently where I used a Synology Drive, and
I set both the drive and my computer for a local backup to DHCP
knowing that there's no DHCP server.
Therefore, they automatically go into the 169.254 range and
do a self‑assignment of an IP address that allows them to
cooperate on the same network.