So now we're going to move forward and talk about DHCPv4 in depth.
Now hopefully if you're taking this particular course,
you know that DHCP stands for the Dynamic Host Configuration Protocol,
or maybe you don't know that you've always just kind of wondered,
regardless, that's what DHCP stands for.
And, as the name implies, it is used for endpoint configuration,
and I say endpoint because it's not necessarily just
workstations that are configured via DHCP.
Just about any network device out there,
whether it's enterprise grade or consumer grade,
uses DHCP to configure them.
If you've ever had to maintain a network that doesn't have DHCP on it,
I pity you first off,
but you will understand why nearly every device out there supports DHCP
because no one wants to manage the IP addresses on 300 or 400
workstations spread across 5 locations and have to worry about wireless
devices moving from location to location,
and it's just a huge mess.
DHCP makes everybody's lives so much simpler,
and again it's used by everybody from ISPs,
they use it to configure their WAN equipment,
if you have a DSL router or a cable modem at home,
it's almost certain that the WAN address on that particular
device is configured via DHCP from the provider.
Now it's almost certain that they tie to the MAC address or
some other identifier on the device so that you can't just
hook up any device on their network,
but you can almost be guaranteed that they're not statically assigning
addresses to everybody's home internet connection.
Enterprises of course use DHCP to configure their workstations,
or other devices out on the WAN.
Again, for my day job I manage workstations at about 12 different locations,
including some users with laptops that move around from various locations
or different subnets within the same location even,
and without a good working DHCP implementation,
again going back to my previous statement,
that management would be much more difficult.
Home routers.
If you've ever seen one, which again,
hopefully at this point in your career you have,
also use DHCP to provide private IP addresses,
and again, that's just for ease of management.
It's so that people that aren't technically adept like you and I,
can simply take their new router home, plug it into their cable modem,
and immediately start using wireless devices or wired devices behind it without
having to go into the management interface and set up DHCP,
and set up a pool, and a scope,
and all this other stuff that you have to do when you set up DHCP.
As I've mentioned, if you don't use DHCP,
static configuration is required,
and not only is that just a pain from a management perspective,
it's also very error prone.
Certainly there's not anyone among us that has not fat
fingered an IP address at one point.
And if you're dealing with any kind of enterprise equipment,
that's just something you really don't have time for,
let DHCP handle all of that.
DHCP started life at BOOTP, or the Bootstrap Protocol,
and you won't see that used very much in modern networks,
with the exception of some diskless workstations like you'd
use for a UNIX-based systems as an example.
Some network card vendors also use a subset of BOOTP in what's called the PXE,
or the Preboot Execution Environment.
We won't be getting into that here because again,
we are focused just on DHCP and how to configure it and what
to do when it doesn't work as expected.
DHCPv4 uses a Client- Server model.
Again, if you've never actually used DHCP or managed it,
you probably figured that out from some of the other references to DHCP
servers and DHCP clients that I've made earlier in this course.
DHCPv4 uses UDP for its transport, and in fact DHCPv6 uses UDP as well,
so I guess this a similarity between both of them.
DHCPv4 uses port 67 for the DHCP server and port 68 for the DHCP client.
You'll see that in the demo section of this particular module when we
actually look at the Wireshark information for a DHCP exchange.
DHCP does use a four-packet exchange,
which we'll talk about here in just a couple of minutes,
and those four packets are generally broadcast packets,
but there are some times where they will use unicast packets,
mainly when you're using DHCP relay agents,
or as Cisco calls them IP helper addresses,
and those IP helper addresses essentially relay these broadcasts
from clients to a centralized DHCP server that sits almost
certainly in a data center some place.
This way you don't have to manage 15 different DHCP
servers running on 15 different routers,
or switches, or servers at all of your branch locations,
you can centralize this at a central location,
and therefore make your management a lot easier.
That also presents a single point of failure,
and so you have to have some redundancy planning in there,
but we're not here to discuss redundancy planning for DHCP,
we're diving deep into the protocol,
but if you're implementing this on your network,
I would definitely take that into consideration.
Finally, you can use DHCP to push out what's called client options.
We'll discuss what some of those are elsewhere in the course,
but both DHCPv4 and DHCPv6 support client options,
and in fact, you can't use DHCP without them,
as you'll see again, when we discuss client options and when we look at in Wireshark.