Assistance with understanding packets in a DHCP request
Posted on 2011-05-12
I am working through a book on TCP/IP and I am currently trying to learn how DHCP works via requests/acknowledgements, etc.
I've got a laptop plugged into a D-link router, via cable. The router is the DHCP server. I am using Microsoft's Network Monitor to capture packets.
I started up the Network Monitor first, and then plugged in the ethernet cable.
I see the initial DHCP request coming from the laptop and I see the acknowledgement from the router. My question pertains to the router acknowledgement.
On the results presented via Network Monitor, the ACK shows the destination h/w address for the acknowledgement (under the ethernet section of the message) as the broadcast address instead of the h/w address of the laptop (which was provided via the initial request broadcast).
In the DHCP specific portion of the ACK packet, the client h/w address is listed.
Why does the router encode the h/w address on the ACK with a broadcast address instead of the previously-provided client h/w address? Doesn't this require the other devices on the network to do extra inspection of the packet since it is sent to a broadcast h/w address vs. being sent directly to the client h/w address? (I understand why the IP portion needs to be broadcast at this point - the laptop doesn't have an IP address just yet).
Sorry if this should be obvious to me. I am just learning. Thanks in advance.