Analysis of grasping package in DHCP process

Through the packet analysis, DHCP four packages are broadcast packets, and the DHCP server, in order to prevent address conflicts, also emits an ARP packet before assigning to the DHCP client address, and if it is a DHCP relay, an ICMP packet is issued.

1.DHCP Client issues DHCP Discover broadcast packet:

Second floor: The Mac of the source Mac---client, the target Mac---FFFF.FFFF.FFFF

Layer three: Source IP---0.0.0.0, target IP---255.255.255.255

2.DHCP receives the DHCP Discover broadcast packet, selects from the address pool from the low to the high to elect the address, and issues the ARP packet:

Second floor: Mac---DHCP service for source Mac, Target mac---FFFF.FFFF.FFFF

3. If you do not receive an ARP response package, you are ready to assign the address to the client, or a second ARP packet will be issued:

4.DHCP client continues to issue DHCP Discover broadcast packet:

Second floor: The Mac of the source Mac---client, the target Mac---FFFF.FFFF.FFFF

Layer three: Source IP---0.0.0.0, target IP---255.255.255.255

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5.DHCP Server response DHCP offer broadcast packet:

Second floor: The Mac of the source MAC---DHCP server, the target mac---FFFF.FFFF.FFFF

Layer three: Source IP---DHCP server IP, target IP---255.255.255.255

6.DHCP Client response DHCP Request broadcast packet:

Two-tier: source MAC---DHCP client mac, Target mac---FFFF.FFFF.FFFF

Layer three: Source IP---0.0.0.0, target IP---255.255.255.255

7.DHCP Server response DHCP ACK broadcast packet:

Second floor: The Mac of the source MAC---DHCP server, the target mac---FFFF.FFFF.FFFF

Layer three: Source IP---DHCP server IP, target IP---255.255.255.255

8.DHCP client receives DHCP ACK broadcast packet, issue unreasonable ARP, confirm that the IP is available, otherwise the DHCP server will continue to request IP:

Two-tier: source MAC---DHCP client mac, Target mac---FFFF.FFFF.FFFF

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