填空题 阅读下面的配置信息，解释(1)～(3)处的命令。
Router1(config)#key chain zhang
Router1(config-keychain)#key 1
Router1(config-keychain-key)#key-string zhang
Router1(config-keychain-key)#exit
Router1(config-keychain)#exit
Router1(config)#interface eth0/0
Router1(config-if-eth0/0)#ip rip authentication key-chain zhang
Router1(config-if-eth0/0)#ip rip authentication mode md5 (1)
Router1(config-if-eth0/0)#ip rip send version 2 (2)
Router1(config-if-eth0/0)#ip rip receive version 2 (3)