reference:
https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol
https://baike.baidu.com/item/DHCP/218195?fr=aladdin#2
https://tools.ietf.org/html/rfc2132
https://tools.ietf.org/html/rfc2131
原文：https://www.cnblogs.com/lianghong881018/p/12165581.html