why dhcp server , sets the destination mac address of dhcp offer & dhcp Ack messeges as Broadcast ?

Question

_{Saturday, October 22, 2011 3:50 AM}

hi all

about dhcp offer and dhcp Ack packets which dhcp server sends to a dhcp client , why although dhcp server knows that client's mac address (by looking at dhcp discover & dhcp request messeges which clint had sent ) , but sets the destination mac address of these packets as Broadcast mac address ( FF-FF-FF-FF-FF-FF ) ?

thanks in advance

All replies (3)

_{Wednesday, October 26, 2011 4:41 AM ✅Answered}

Hi John,

Thanks for your reply.

Below is a packet-level description of the conversation process:

From your post, I understand that you need to know why we know the destination MAC address but still use (FF-FF-FF-FF-FF-FF) as a destination. I’d like to explain that all packets must have IP address of the source and destination. If we don’t know the destination IP address exactly, we can only broadcast the packet (use 255.255.255.255 as a destination). Since we do not have any IP for the client, so the DHCP server must broadcast the DHCPOFFER & DHCPACK. This is by design, you may refer to the standard protocol defined by RFC 2131. Your understanding is appreciated.

Dynamic Host Configuration Protocol

http://www.ietf.org/rfc/rfc2131.txt

Best Regards,

Aiden

_{Monday, October 24, 2011 7:32 AM}

Hi,

Q: Why DHCP server, send DHCPOFFER & DHCPACK messages as Broadcast?

A: Because the client does not yet have a IP address assigned to it and can only receive broadcast traffic. Please keep in mind that the client cannot assume the IP address in the offer until it receives DHCPACK. Since transport protocol must has the IP address of the source and destination. So the DHCP server must broadcast the DHCPOFFER/DHCPACK to every client.

For detailed conversation between DHCP client and DHCP server, you may refer to the following link:

DHCP (Dynamic Host Configuration Protocol) Basics

http://support.microsoft.com/kb/169289

Best Regards,

Aiden

_{Tuesday, October 25, 2011 9:49 AM}

Hi,

 

Q: Why DHCP server, send DHCPOFFER & DHCPACK messages as Broadcast?

A: Because the client does not yet have a IP address assigned to it and can only receive broadcast traffic. Please keep in mind that the client cannot assume the IP address in the offer until it receives DHCPACK. Since transport protocol must has the IP address of the source and destination. So the DHCP server must broadcast the DHCPOFFER/DHCPACK to every client.

 

For detailed conversation between DHCP client and DHCP server, you may refer to the following link:

DHCP (Dynamic Host Configuration Protocol) Basics

http://support.microsoft.com/kb/169289

 

 

Best Regards,

Aiden

hi  Aiden ,

pay atention to my question ,

my question was about  destination mac address and not destination ip address.

now any idea plz