手動配置ip浪費時間，容易出錯，而且毫無擴充套件性
dhcp根據使用者vlan屬性（即閘道器匹配），位址被自動的指定分配
通過和中心位址的關聯，使得整個組織有連續的和層次化的結構
1. s：0.0.0.0 d: 255.255.255.255
2. s:dhcp伺服器 d:255.255.255.255
3. s:0.0.0.0 d255.255.255.255
4. s:s:dhcp伺服器 d:255.255.255.255
sw1(config)#do show run | s pool
ip dhcp pool vlan10
network 10.1.10.0 255.255.255.0
default-router 10.1.10.254
dns-server 114.114.114.114
domain-name marketing
lease 1 12
sw1(config)#ip dhcp excluded-address 10.1.10.250 10.1.10.254
pc1(config)#default int e0/1
pc1(config)#int e0/1
pc1(config-if)#no shu
pc1(config-if)#ip add dhcp
pc1(config-if)#exit
pc1(config)#no ip routing
pc1(config)#ip default-gateway 10.1.10.254
pc1(config)#exit
sw1(config)#do show ip dhcp pool
pool vlan10 :
utilization mark (high/low) : 100 / 0
subnet size (first/next) : 0 / 0
total addresses : 254
leased addresses : 1
excluded addresses : 5
pending event : none
1 subnet is currently in the pool :
current index ip address range leased/excluded/total
10.1.10.3 10.1.10.1 - 10.1.10.254 1 / 5 / 254
sw1#show ip dhcp conflict
ip address detection method detection time vrf
sw1#clear ip dhcp conflict *
pc1#debug dhcp
pc1(config)#int e0/1
pc1(config-if)#shu
*sep 22 16:11:41.383: dhcp: deleting entry b1c6f278 10.1.10.1 from list
*sep 22 16:11:41.383: dhcp: client socket is closed
pc1(config)#int e0/1
pc1(config-if)#no shu
*sep 22 15:38:36.439: rac: starting dhcp discover on ethernet0/
*sep 22 15:38:36.453: b'cast on ethernet0/1 inte***ce from 0.0.0.0
*sep 22 15:38:38.461: dhcp: received a bootrep pkt
*sep 22 15:38:38.461: dhcp: offer received from 10.1.10.254
*sep 22 15:38:38.461: dhcp: srequest- server id option: 10.1.10.254
*sep 22 15:38*sep 22 15:38:38.462: dhcp: received a bootrep pkt
*sep 22 15:38:42.486: dhcp: sending notification of assignment:
*sep 22 15:38:42.486: address 10.1.10.2 mask 255.255.255.0
pc1#undebug all
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