初识CISCO_DHCP Server

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　　#ip dhcp pool global
　　(dhcp-config)#domain-name nhq.com
　　(dhcp-config)#network 192.168.1.0 255.255.255.0
　　(dhcp-config)#lease 7
　　ip dhcp pool global
　　network 192.168.1.0 255.255.255.0
　　domain-name nhq.com
　　default-router 192.168.1.254
　　lease 7
　　上面几步做好就能使用DHCP Server了，但是这做的并不全面，比如做绑定，给网段分不同地址等都还没做；我GNS3上面模拟的CISCO 3600路由器，没找到Vlan的地址分配配置；
　　再贴一个DHCP Server服务的请求过程：
　　VPCS[1]> dhcp -d
　　Opcode: 1 (REQUEST)
　　Client IP Address: 0.0.0.0
　　Your IP Address: 0.0.0.0
　　Server IP Address: 0.0.0.0
　　Gateway IP Address: 0.0.0.0
　　Client MAC Address: 00:50:79:66:68:00
　　Option 53: Message Type = Discover
　　Option 12: Host Name = VPCS1

　　Option 61: Client>　　68:00
　　第一次请求，客户端并没有获取到IP地址
　　Opcode: 2 (REPLY)
　　Client IP Address: 0.0.0.0
　　Your IP Address: 192.168.1.1
　　Server IP Address: 0.0.0.0
　　Gateway IP Address: 0.0.0.0
　　Client MAC Address: 00:50:79:66:68:00
　　Option 53: Message Type = Offer
　　Option 54: DHCP Server = 192.168.1.254
　　Option 51: Lease Time = 604394
　　Option 58: Renewal Time = 302197
　　Option 59: Rebinding Time = 528844
　　Option 1: Subnet Mask = 255.255.255.0
　　Option 15: Domain = nhq.com
　　Option 3: Router = 192.168.1.254
　　第一次答复，DHCP服务器做的答复，分配给客户机一个192.168.1.1的地址，DHCP Server地址为192.168.1.254
　　Opcode: 1 (REQUEST)
　　Client IP Address: 192.168.1.1
　　Your IP Address: 0.0.0.0
　　Server IP Address: 0.0.0.0
　　Gateway IP Address: 0.0.0.0
　　Client MAC Address: 00:50:79:66:68:00
　　Option 53: Message Type = Request
　　Option 54: DHCP Server = 192.168.1.254
　　Option 50: Requested IP Address = 192.168.1.1

　　Option 61: Client>　　68:00
　　Option 12: Host Name = VPCS1
　　客户端第二次请求，已经获取到IP地址
　　Opcode: 2 (REPLY)
　　Client IP Address: 192.168.1.1
　　Your IP Address: 192.168.1.1
　　Server IP Address: 0.0.0.0
　　Gateway IP Address: 0.0.0.0
　　Client MAC Address: 00:50:79:66:68:00
　　Option 53: Message Type = Ack
　　Option 54: DHCP Server = 192.168.1.254
　　Option 51: Lease Time = 604800
　　Option 58: Renewal Time = 302400
　　Option 59: Rebinding Time = 529200
　　Option 1: Subnet Mask = 255.255.255.0
　　Option 15: Domain = nhq.com
　　Option 3: Router = 192.168.1.254
　　IP 192.168.1.1/24 GW 192.168.1.254
　　DHCP服务器第二次答复，确认IP地址已经被分配掉
　　这里我们可以从Option 53这一行看到数据包的状态，从Discover到Offer再到Request最后到Ack；
　　一次DHCP请求就这样结束了