单项选择题 The output of the show aaa domain-map displays the following information: Domain: isp1.com; virtual-router: vr1; loopback: 1 Domain: isp2.com; virtual-router: vr2; loopback: 1 Domain: none; virtual-router: vr3; loopback: 1 Domain: default; virtual-router: vr4; loopback: 1 The end user supplies a login name of joe with no domain name. Which virtual router is responsible for authenticating this user?（）

单项选择题 When does the E-series router start monitoring DHCP traffic using the DHCP External function?（）

单项选择题 Which CLI command is used to display the IP address assigned to Dynamic Subscriber Interface and related hardware address using the DHCP Relay Proxy function?（）