DHCP客户端与DHCP服务器通信过程

一、客户端向服务器请求ip地址

1.客户端ip地址是0.0.0.0，广播DHCP discover

"299","295.584998","0.0.0.0","255.255.255.255","DHCP","DHCP Discover - Transaction ID 0x29572ad"

       DHCP server检测给客户端提供的ip地址是否有客户端已占用

300  295.630175    ca:00:16:00:00:00   Broadcast       ARP       Who has 10.10.0.4?  Tell 10.10.0.1

2．DHCP server（10.10.0.1）发送广播提供DHCP offer

302  297.588139    10.10.0.1 255.255.255.255    DHCP     DHCP Offer    - Transaction ID 0x29572ad

Client IP address: 0.0.0.0 (0.0.0.0)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

此时客户端ip是0.0.0.0，服务器预提供的ip是10.10.0.4

3.    客户端发送广播请求地址10.10.0.4

303  297.628176    0.0.0.0    255.255.255.255    DHCP     DHCP Request  - Transaction ID 0x29572ad

       Option: (t=50,l=4) Requested IP Address = 10.10.0.4

4.    服务器广播ACK给该客户端，此时客户端扔无ip地址

304  297.677889    10.10.0.1 255.255.255.255    DHCP     DHCP ACK      - Transaction ID 0x29572ad

Client IP address: 0.0.0.0 (0.0.0.0)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

       客户端检查分配给自己的ip地址是否和其他客户端冲突

Vmware_c0:00:03  Broadcast       ARP       Gratuitous ARP for 10.10.0.4 (Request)（连续3次）

客户端获取DHCP服务器MAC地址，因为下面要进行单播通信

Vmware_c0:00:03  Broadcast       ARP       Who has 10.10.0.1?  Tell 10.10.0.4

ca:00:0f:2c:00:00   Vmware_c0:00:03  ARP       10.10.0.1 is at ca:00:0f:2c:00:00

5.         客户端向DHCP服务器发送正式的请求

130  67.478249      10.10.0.4 10.10.0.1 DHCP     DHCP Request  - Transaction ID 0xeb9392dc

Client IP address: 10.10.0.4 (10.10.0.4)

Your (client) IP address: 0.0.0.0 (0.0.0.0)

6.         DHCP服务器发送ACK给客户端

131  67.550820      10.10.0.1 10.10.0.3 DHCP     DHCP ACK      - Transaction ID 0xeb9392dc

Client IP address: 10.10.0.4 ( 10.10.0.4)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

 

二、客户端释放ip地址

21    26.987415      10.10.0.4 10.10.0.1 DHCP     DHCP Release  - Transaction ID 0xc89dd936

 

三、客户端第二次向服务器请求ip地址

1.客户端地址0.0.0.0 发送广播

112  200.816873    0.0.0.0    255.255.255.255    DHCP     DHCP Discover - Transaction ID 0x9227fa07

服务器检测是否该地址被占用

113  200.852968    10.10.0.1 10.10.0.4ICMP      Echo (ping) request（2次）

2.服务器向10.10.0.4发送单播

Ethernet II, Src: ca:00:0f:2c:00:00 (ca:00:0f:2c:00:00), Dst: Vmware_c0:00:03 (00:50:56:c0:00:03)

116  202.832590    10.10.0.1 10.10.0.4 DHCP     DHCP Offer    - Transaction ID 0x9227fa07

Client IP address: 0.0.0.0 (0.0.0.0)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

3.    客户端发送广播请求地址10.10.0.4

117  202.832831    0.0.0.0    255.255.255.255    DHCP     DHCP Request  - Transaction ID 0x9227fa07

4.    服务器广播ACK给该客户端，此时客户端仍无ip地址

304  297.677889    10.10.0.1 10.10.0.4 DHCP     DHCP ACK      - Transaction ID 0x29572ad

Client IP address: 0.0.0.0 (0.0.0.0)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

       客户端检查分配给自己的ip地址是否和其他客户端冲突

Vmware_c0:00:03  Broadcast       ARP       Gratuitous ARP for 10.10.0.4 (Request)（连续4次）

客户端获取DHCP服务器MAC地址，因为下面要进行单播通信

Vmware_c0:00:03  Broadcast       ARP       Who has 10.10.0.1?  Tell 10.10.0.4

ca:00:0f:2c:00:00   Vmware_c0:00:03  ARP       10.10.0.1 is at ca:00:0f:2c:00:00

7.         客户端向DHCP服务器发送正式的请求

130  67.478249      10.10.0.4 10.10.0.1 DHCP     DHCP Request  - Transaction ID 0xeb9392dc

Client IP address: 10.10.0.4 (10.10.0.4)

Your (client) IP address: 0.0.0.0 (0.0.0.0)

8.         DHCP服务器发送ACK给客户端

131  67.550820      10.10.0.1 10.10.0.3 DHCP     DHCP ACK      - Transaction ID 0xeb9392dc

Client IP address: 10.10.0.4 (10.10.0.4)

Your (client) IP address: 10.10.0.4 (10.10.0.4)

 

客户端向服务器请求ip地址的不同在于首次请求ip地址时服务器offer和ack包是广播地址，服务器把客户端信息记录下来，当客户端再次接入网络获取地址时，服务器对该客户端发送单播包。

转载于:https://blog.51cto.com/walkinginthesun/249905