Cisco - CCENT/CCNA R&S (100-105) - DHCP - Dynamic Host Configuration Protocol - Overview .37

Thirty-Seventh Video in a Series covering all elements of The Cisco Certified Entry Networking Technician (CCENT) 100-105 ICND1v3 which is the first part of the CCNA certification.

Blueprint Section: Infrastructure Services

The first video within the Infrastructure Services section of the CCENT 100-105 blueprint and we jump straight into DHCP the Dynamic Host Configuration Protocol.

We start by understanding that DHCP is a protocol which allows our host to automatically obtain an IP address when connecting to the network. We review the DORA process; Discover, Offer, Request and Acknowledgement.

We said DHCP servers are normally inside the broadcast domain of the host they’re serving as DHCP heavily uses broadcast messages. However, it’s certainly possible to have a central DHCP server and setup devices in our network to relay the DHCP messages across the broadcast domain boundary to remove destinations.

Remember DHCP can be setup in three different flavours on our Cisco routers: Client, Server and Relay. Ensure you understand the differences between them

In our next video, we setup all the variants for DHCP

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[tomb]

Sey Says
" Jul 6, 2011 8:03 AM (in response to Sanjay Singh)
The client sends DHCPDiscover. It is broadcast both in Layer 2 and Layer 3.
The server replies with DHCPOffer. It's broadcast in Layer 3 but unicast in Layer 2.
The client replies with DHCPRequest. It's broadcast in both Layers 2/3.
The server sends DHCPAck. It's broadcast in Layer 3 but unicast in Layer 2.


As you see, at Layer 3 all communication is broadcast. This makes sense as the client does not have an IP address. However, what many people overlook is both client and server have Layer 2 (i.e. MAC) addresses, so unicast communication is possible at Layer 2.



At Layer 2, the client's messages are always broadcast, and those of the server's can be unicast or broadcast depending on how vendor implemented it."

[ericbirtel]

Passed CCENT yesterday! These videos were a big part of it.

[narendrareddy]

Hello, Ryan Beney.
First of all.
I passed my ICND1 yesterday.
Thanks to you.
I'm still going to watch the videos you'll be making in this series.. You're doing excellent job. Keep it up mate.
Even though I wasn't able to fully utilize your channel (I found it during the last stage of my prep), It helped a lot.
I have to say this bro. After covering your video focusing on subnetting, and with a little practice.I can freaking do any conversion in less than 10s without a pen & paper.
Lastly, I think you should really go into professional teaching. I have paid for videos that didn't offer 1/3 of what you're producing. If you are focusing on a teaching career. Mark my words, you'll go great lengths.
Have a great day.
👍

[cyborgdale]

I had to laugh when you mentioned D.O.R.A. as I came up with this mnemonic myself as well. I had not seen it used anywhere else and thought that I was original. I think of it as "DORA the explorer" since it "explores" for an IP address, etc. It is the host that initializes the exchange with the "Discover" packet.

[ericbirtel]

Thanks for another great video Ryan. CCENT Exam in 2 days, and have watched all of yours several times, as well as a few other resources. To the point, good information, and you present the topics in an easy to understand format.

[dean]

Wow an actual videos for the current (CCENT) 100-105 ICND1. I am subscribing!

[yummypie]

That packet life website is fantastic thanks for showing it.

[leandrorodriguez]

I enjoy your videos very much. Probably the best Cisco course I have came across. I just wish you continued doing them. I'm hoping to see more soon. Great job !

[arashemami]

Hi Ryan, Thanks alot for your great Tutorial, I have never heard DORA before and i used to forget the process of DHCP but I think with this word i can always have the DHCP Process in my mind.

[rybot]

Writing CCENT for the fourth time tomorrow! I've used a few other good resources as well but I always find myself back watching your latest releases on the eve of terror. Thanks again Ryan!

[Kleedje]

I passed the CCENT today, your video' played a very very big part of that. I want to thank you for these video's. Your type of teaching/explaining topics just fits my personal need perfectly. And I hope you will continue to create video's in the Future. I'm even willing to pay for it without doubt.

For the other people studying CCENT or CCNA. I offcourse used other sources to study. The book, other random internet searches an single practice test I gained access for when purchasing the book.

[ahmedabdulla]

Thank you for this video, keep going .

[BeigeRageProductions]

Do we need to know about IP Helper addresses for the CCENT exam? You mentioned "relays" which provide a similar capability, but you didn't mention IP Helper configuration. Great videos by the way.

[abdulrahmansworld]

Hi mr ryan will u continue to ICND 2 to complete CCNA course? please answer.

[michaeltagg]

Hi Ryan 13:10, is an acknowledgement broadcast or unicast?

Can't seem to find a clear answer on the web for this, assuming dhcp is local and no relay involved.... Is unicast involved at any DORA process?

Discover= Broadcast. Makes sense, host doesn't know where DHCP server it is, sends it mac address as source. L3 DST 0.0.0.0 with L2 DST all Fs broadcast.

Offer= L3 Broadcast because the device doesn't have an IP destination yet, so it needs to be blank with all 0's, but L2's host destination as source, so we still call it a broadcast? DST IP 0.0.0.0 with DST MAC A1:B2:C3:D4:E5:D6 etc

Request= Broadcast, even though the PC is now aware of the DHCP servers IP address? I've read that the request broadcast is done to alert other DHCP servers to cancel/reject their offers, is this right?

Acknowledgement= Broadcast? The server now has an address for the host, but the host doesn't know to actually use it yet until the acknowledgement is done. Is this right or was the IP assumed with the request?

TLDR: Are they all broadcasts?