In data link layer, we solved three problems by improving the ARP protocol. As follows: 1. The transparent mode is realized. And the troubles of firewall management in different subnet are solved.

• 在数据链路层,通过对ARP协议的改进,解决了以下三个问题:(1)实现了透明模式,并采用ARP代理技术,解决了防火墙跨网段管理的问题。