找出你的DHCP Server

方法一：

從你的log紀錄，可以獲得區域網路內提供你 DHCP 服務的機器位址

sudo grep -r "DHCPOFFER" /var/log/* | grep "$(export LC_ALL=C; date +'%b %d')" | tail -1

方法二：tcpdump + dhclient

sudo tcpdump -i wlp4s0  -pvn port 67 and port 68
dhclient 你的網路介面

方法三：使用 nmap (推薦，可掃出區網的DHCP Server)

sudo nmap --script broadcast-dhcp-discover -e wlp4s0

Starting Nmap 7.60 ( https://nmap.org ) at 2019-12-21 11:51 CST
Pre-scan script results:
| broadcast-dhcp-discover: 
|   Response 1 of 1: 
|     IP Offered: 192.168.43.102
|     DHCP Message Type: DHCPOFFER
|     Server Identifier: 192.168.43.1
|     IP Address Lease Time: 1d00h00m00s
|     Renewal Time Value: 12h00m00s
|     Rebinding Time Value: 21h00m00s
|     Subnet Mask: 255.255.255.0
|     Router: 192.168.43.1
|_    Domain Name Server: 192.168.43.1, 192.168.43.1
WARNING: No targets were specified, so 0 hosts scanned.
Nmap done: 0 IP addresses (0 hosts up) scanned in 0.47 seconds