Dynamic Host Configuration Protocol (DHCP)
Summary
TLDRThis lecture delves into the process of obtaining IP addresses, focusing on the Dynamic Host Configuration Protocol (DHCP). It explains how DHCP dynamically assigns IP addresses to devices joining a network, facilitating a seamless connection experience. The lecture outlines the DHCP process, starting from the client's DHCP discover message to the server's offer and the client's request, culminating in the server's acknowledgement. It also touches on the additional information DHCP can provide, such as the default gateway and subnet mask. The lecture further explains how a network obtains its IP address from an Internet Service Provider (ISP), who in turn gets its IP addresses from the Internet Corporation for Assigned Names and Numbers (ICANN).
Takeaways
- 💻 IP addresses can be manually set by a system administrator or automatically obtained through DHCP (Dynamic Host Configuration Protocol).
- 🔄 DHCP is a protocol that dynamically assigns IP addresses to devices joining a network, making it a 'plug and play' solution.
- 📡 DHCP supports mobile users by providing temporary IP addresses, which can be reused once the device leaves the network.
- 📢 The DHCP process involves four main steps: DHCP Discover, DHCP Offer, DHCP Request, and DHCP Acknowledgement.
- 🖥️ When a client enters a network, it broadcasts a DHCP Discover message to find a DHCP server, which responds with an IP address offer.
- 🌐 DHCP servers use ports 67 and 68 for communication, and they broadcast messages to ensure the client without an IP address receives them.
- 🔑 DHCP not only provides IP addresses but also other network configuration details like the subnet mask and default gateway.
- 🌐 The DHCP server obtains its pool of IP addresses from an ISP (Internet Service Provider), which manages large blocks of IP addresses.
- 🏢 Organizations receive their IP address blocks from ISPs, which are part of a larger allocation managed by the ISP.
- 🌐 ISPs get their IP address allocations from the IANA (Internet Assigned Numbers Authority), which oversees global IP address distribution.
Q & A
What is the primary function of DHCP?
-The primary function of DHCP (Dynamic Host Configuration Protocol) is to automatically assign IP addresses to devices on a network, ensuring that each device has a unique address without manual configuration.
How does a device obtain an IP address without manual configuration?
-A device obtains an IP address without manual configuration through DHCP, which assigns an IP address dynamically from a server when the device joins the network.
What is the purpose of the DHCP Discover message?
-The DHCP Discover message is a broadcast message sent by a client entering a network to identify available DHCP servers that can provide an IP address.
Why does the DHCP server respond with a broadcast message?
-The DHCP server responds with a broadcast message because the client, having just entered the network, does not yet have an IP address, and thus cannot be reached through a unicast message.
What information does DHCP provide to a client besides an IP address?
-Besides an IP address, DHCP can also provide the client with the address of the first hop router, the name and address of the DHCP server, and the subnet mask of the network.
How does a client indicate acceptance of the IP address offered by the DHCP server?
-A client indicates acceptance of the offered IP address by sending a DHCP Request message, which is a broadcast message, to the DHCP server.
What are the two main ports used for DHCP communication?
-The two main ports used for DHCP communication are port 67 (used by the DHCP server) and port 68 (used by the DHCP client).
How does a network obtain its IP addresses from an ISP?
-A network obtains its IP addresses from an ISP (Internet Service Provider), which allocates a block of IP addresses to the network based on the organization's requirements.
What is the role of the Internet Corporation for Assigned Names and Numbers (ICANN) in IP address allocation?
-ICANN is responsible for coordinating the allocation of IP addresses. ISPs can obtain IP addresses by requesting them from ICANN, which manages the global distribution of IP address space.
What is the significance of the subnet mask in DHCP?
-The subnet mask in DHCP is significant as it defines the network portion of an IP address, allowing the DHCP server to correctly allocate IP addresses within the designated subnet.
How does the DHCP server know which IP addresses to hand out to clients?
-The DHCP server knows which IP addresses to hand out based on the subnet information it has been configured with, which is typically provided by the ISP and includes a range of IP addresses for分配 to clients.
Outlines
🌐 Understanding IP Address Acquisition
This paragraph introduces the concept of obtaining an IP address, which can be manually set by a system administrator or automatically assigned through a protocol called DHCP (Dynamic Host Configuration Protocol). The lecture explains that most users connect to networks seamlessly due to DHCP, which dynamically assigns IP addresses to devices joining a network. The process involves the client broadcasting a DHCP discover message to find a DHCP server, the server responding with a DHCP offer message, the client requesting the IP address, and the server acknowledging the request. An example scenario is provided where a client enters a network and communicates with a DHCP server to obtain an IP address. The paragraph also touches on the temporary nature of IP addresses assigned by DHCP, which can be reused by other devices once the original device leaves the network.
📡 Deep Dive into DHCP Operations
The second paragraph delves deeper into the workings of DHCP, explaining that it not only provides IP addresses but also other network configuration details such as the address of the first hop router and the subnet mask. It outlines the communication process using UDP on ports 67 and 68, detailing how a client sends a DHCP request, the server responds with a DHCP offer, and the client acknowledges the offer. The paragraph also discusses how DHCP servers obtain their pool of IP addresses from ISPs (Internet Service Providers), which in turn get their addresses from the Internet Corporation for Assigned Names and Numbers (ICANN). The lecture concludes with a mention of a DHCP lab where students can explore these concepts practically.
Mindmap
Keywords
💡IP Address
💡Subnetting
💡DHCP
💡DHCP Discover Message
💡DHCP Offer Message
💡DHCP Request
💡DHCP Acknowledgement
💡Broadcast Message
💡UDP
💡ISP
💡ICANN
Highlights
Introduction to obtaining an IP address through manual configuration or DHCP.
Explanation of how to hardcode an IP address in Windows, Unix, and Mac systems.
The convenience of connecting to a network without manual IP configuration due to DHCP.
Definition and purpose of the Dynamic Host Configuration Protocol (DHCP).
DHCP's role in providing IP addresses dynamically and supporting mobile users.
The process of DHCP: from DHCP Discover to DHCP Acknowledge.
Example of DHCP message exchange between a client and a server.
The significance of subnets in DHCP and how clients are assigned IP addresses within them.
Technical details of DHCP message broadcasting and port usage (67 and 68).
How DHCP provides additional network configuration information beyond IP addresses.
The protocol stack's role in DHCP message transmission and reception.
DHCP lab exercise overview for practical understanding.
How networks obtain IP addresses from ISPs and the role of subnetting.
The allocation of IP addresses by the Internet Corporation for Assigned Names and Numbers (ICANN).
Summary of IP address allocation from ISPs to organizations and the role of ICANN.
Conclusion and wrap-up of the lecture on IP addresses.
Transcripts
hello everyone in the last lecture we Le
we talked about IP addresses and and
subance in this lecture we're going to
talk about how to obtain an IP address
so an IP address can be hardcoded uh
into hardcoded by the system admin in a
file for example you could hardcode your
IP address in Windows Unix Mac in
Windows all that you have to do is go to
the control panel the network
configuration go to TCP IP and set
properties where you can actually give
your IP address but most of you would
have noticed that you have never done
anything like this you've just opened
your laptop and you've been able to
seamlessly connect to the network that's
because of a protocol called DCP which
is dynamic host configuration protocol
it helps host obtain add D IP addresses
dynamically from the server so it's kind
of a plug andplay protocol so
let's look into the details about
DCP okay so goal of DCP is to uh provide
host IP address
from the network server whenever the
host joins the network and uh if it can
renew uh DP also helps host to renew
their IP
addresses what it's what it supports it
supports mobile users because if
whenever mobile users who want to join a
network they need an IP address only for
a short duration of time and H DHCP
would help uh give an IP address to
these host and once the host uh leave
the network this IP address can be used
for some other uh some other host which
then end enters the network so how does
DHCP work the first the host broadcast a
DHCP discover message this is this is
basically the host that's entering the
network it's sending out a DHCP discover
message basically trying to find out
where the DHCP server is or if there is
a DHCP server the DHCP server then
responds with the DHCP offer message
then the host sends a request an IP
address from the DHCP server and the
message is a dhp request and then the
DHCP server sends a DHCP acknowledgement
message with and basically it sends the
address to the uh to the host okay so
let's uh look at it via an example so
here is a client which is entering this
network uh and here is a DHCP server so
as you can see there are three
particular subnets in this uh in this
network and the client is entering this
particular subnet out here which is
22312 do0
sl24 okay so once the client enters the
network what the client does is it sends
a DHCP discover message basically the
DHCP disc discover message is a
broadcast message and it asks is if a
DHCP server is out there so and sends a
broadcast message and because the client
is just entering the network it does not
have an IP address you can see that the
source IP address is 0.0.0.0 the
destination of this address is
255.255 25525 5 which is basically all
once that is how a broadcast message is
sent because the client does not
currently know what the IP address is of
the DCP server so it sends a broadcast
message and the ports that are used for
DC by DHCP for communication are 67 and
68 okay so once the DHCP discover
message is sent to the server the server
responds with a DHCP offer message
basically that is also a broadcast
message and saying and it says to the
client that I am this DCP server and
here here is an IP address that the
client could use so why does the server
need to send a broadcast message the
reason is the client currently does not
have an IP address so the only way that
the server could reach this particular
client is if it sent a broadcast message
for all the hosts in the net which all
the hosts in the network could could
receive so it sends this broadcast
message so basically as you can see here
the source address is a source address
of this DHCP server which is 22312 do5
and the destination is again all mons
and what it this y i a address basically
is
22312 do4 basically what this DCP server
is saying that this client could
potentially use this IP address if it
wants to then the client just says sends
another broadcast message saying that it
would accept the this this IP address
and then the DHCP server basically sends
an acknowledgement back saying that it
has the acknowledging that the cl client
could take the IP address and it just
makes a note of the fact that one client
in the network has this IP address which
is 22312 do4 which makes sure that it
does not provide the same IP address to
another client which arrives into the
network in
Future Okay so let's now go into
a little more more detail DCP the
primary job of DHCP is to provide IP
addresses but that's not the only thing
that DHCP does DCP could provide the
address of the first hop router for a
client it can also provide the name and
address of the DCP server from further
it also provides a net uh the network MK
basically the the subnet mask of the the
subnet portion of the of the network
okay so how does DCP work so we looked
at the Discover and uh the Discover the
offer the request and the response
messages but what protocol does DCP use
so basically when a client arrives in
this network what it does is it's want
to send a DHCP message so it want
basically wants to obtain a IP address
so it will use ghcp so it sends this
DHCP request this DCP request is sent
using UDP so it sent using UDP and it
travels on the all the way down through
this protocol stack and then it's sent
onto this network where this server the
DHCP server
actually receives it you can make sure
you can understand that because uh the
destination is all set to to one because
otherwise or FFF FFF here on the land
that's just the just a broadcast message
how a broadcast me propagates an
Ethernet and then the uh DCP server is
going to receive this message then
what's going to happen is the DCP server
message is going to travel up the
protocol stack at the server and
basically it's going to get
demultiplexed and then the and then the
DHCP server is basic Bally going to send
an acknowledgement back to the to the
client where it's once again going to
travel up the protocol stack after all
this the client is basically going to
have an an IP address or it's it can
also have the name of the first hop
router and the name of this DCP server
so these are this these are the things
that the client can obtain uh using DCP
from the server okay so as I said can
know this IP address and also know the
IP address of it's first stop
okay so we in in your Labs you'll be
doing a DHCP lab and this is how and if
you use wiot this is how a DCP request
message is going to look like and this
is how a DCP response uh reply message
is going to look like so I just wanted
to give you a high level overview of how
it looks like and you'll be do working
out the wi shock labs for yourself okay
so far we looked at how an um an
individual host can obtain an IP address
the next question is how does a net
Network obtain an IP address the DCP
server can hand out IP addresses to the
different clients but then the question
is how does DCP server know which
addresses to hand out basically it
should know the DHCP server has to know
the subnet part of the IP address right
so the qu the answer to this question is
a network obtains its IP address from
the ISP so the ISP has a bunch of IP
addresses that can that can hand out and
hands it out to the different
organizations for example here this
isp's block of IP address is 200231 16.0
sl20 so the first 20 bits are the subnet
the remaining bits could be the host it
just divides the block of IP addresses
it has to the different organizations
which request IP addresses from it for
example to the organization zero it
gives 200231 16.0 sl23 to organization 1
it gives 200231
18023 and so on this is how
organizations obtain their IP addresses
from the
ISP of course you will now be thinking
that how can ISP obtain the IP address
so this is basically the the last word
we're going to talk about IP addressing
basically an ISP can get an its IP
address from the I can basically the
internet Corporation for assigned names
and numbers it's an organization which
allocates IP addresses and an ISP can
actually obtain IP addresses by going
and requesting IP addresses from on the
I can with that I I'll wrap up our
discussion on IP addresses thank you all
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