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I'm learning about the DORA process in TCP IP. And the way server communicates with client is very "confusing" to me.

Let's take an example of DHCP Offer: At this point, the client is still not having its IP address. But in wireshark, the destination address is shown as the "client's to be ip address". How will a packet be routed to a non-existent IP address?

Likewise in case of acknowledgement packet, are we really routing by IP address? Because here also destination IP is the IP of client assigned by server which I believe the client hasn't really get it.

Is there a precedence of addressing that takes place, for example: if there is MAC address then route by MAC address or something like that.

If yes, Who defines the routing precedence?

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  • Yes, normal routing is by destination IP address exclusively. Neither MAC address nor TCP ports etc. are relevant. Please add further details to your question to what you see or where you're having problems understanding.
    – Zac67 ♦
    Commented Feb 8 at 11:20
  • Edited to my best of knowledge @Zac67. I am really confused in learning as I want to go in unnecessary depth, you've got some words of wisdom for people like me?
    – Team B.I
    Commented Feb 8 at 14:26

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DHCP without relay isn't routed, so the DHCP client can always be addressed by its MAC address (in CHADDR) through switching (=L2 forwarding).

Relayed DHCP can be routed (=forwarded on L3) between the relay agent and the DHCP server via the agent's IP address.

Protocols above the transport layer like DHCP itself are explicitly off topic here, see the help center. You might want to read RFC 2131 and RFC 3046 though.

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  • I've added an image in the post, where you can see(you can see wireshark dhcp packet sample as well) something. You say that the IP is of relay and it forwards the packet based on MAC address. But later you observe the packets, the IP of the client will be the IP of the relay. How so?
    – Team B.I
    Commented Feb 8 at 14:43
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    I don't see any relay there. DHCP Offer and ACK are simply returned as unicast to the MAC address indicated in the Discovery's CHADDR field. Alternatively, a client may request broadcast Offer and ACKs using the BROADCAST flag in its Discovery.
    – Zac67 ♦
    Commented Feb 8 at 15:08

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