DHCP Sequences: Broadcast vs. Unicast

I missed a sequence diagram for DHCP which not only shows the four basic messages (DISCOVER, OFFER, REQUEST, ACK), but also the used source/destination addresses and ports, the type of connection (unicast/broadcast), the differences between the initial and the renewing messages, and the needed firewall rules for allowing DHCP traffic to/from the own interface or to/from a DHCP relay agent.

Here it comes! :)

DHCPv4 Message Sequence Diagram

If there are any mistakes -> send me a comment.

DHCP Sequences and Messages

Or download it as PDF


Security Policy on a Palo Alto

One quick example: With the usage of bidirectional policy rules on a Palo Alto, the only security policy needed for the whole DHCP setup is the following (DHCP between the DHCP server and the network – and vice versa):

DHCP Palo Alto Rule

Featured image “Bald Eagle Fishing Sequence” by Lorne Sykora is licensed under CC BY-NC-ND 2.0.

2 thoughts on “DHCP Sequences: Broadcast vs. Unicast

  1. Hello Johannes,

    I have a strange DHCP issue with my SRX Juniper firewall and my both PCs one of them windows 8 and the second one is windows 7 .

    the second one (win7) does not have any problem with getting IP . but the first one (win8) does have a problem, it does not get IP from the SRX firewall.

    I’m sure the I have configured DHCP right in the SRX .
    master@SRX> show configuration system services dhcp | display set
    set system services dhcp pool address-range low
    set system services dhcp pool address-range high
    set system services dhcp pool maximum-lease-time 3600
    set system services dhcp pool default-lease-time 3600
    set system services dhcp pool name-server
    set system services dhcp pool name-server
    set system services dhcp pool router
    set system services dhcp propagate-settings ge-0/0/0.0

    I have does too many troubleshooting in my win8PC :
    1- netsh reset command
    2- disable / enable to the LAC
    3- remove and install again to the LAC
    4- assured if the IPv4 optioned is checked
    5- rebooting the PC
    6- tried with another RJ45 cable

    on the same interface I put the win7 PC , and it WORKED ! .. but when I put the win8 it does not .
    I’ve tried with another win8 PC , to see if the bug is in the first win8 pc , But guess what .. it also didn’t work ! :\

    Do you have any idea what the solution might be ?

    thanks in advance :)

    1. Hi Abed,
      I am sorry, but I cannot help you with this issue. So far I have not troubleshooted Win 8 DHCP problems, nor SRX DHCP problems. I am sorry.

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