多项选择题 You are a senior network administrator at TestKing and your trusty junior administrator tells you that he failed his task of adding VLAN 50 to a Catalyst switch in the network. You enter in the show vtp status command and get this output: TK2# show vtp status VTP Version :2 Configuration Revision :7 Maximum VLANs supported local :68 Number of existing VLANs :8 VTP Operating Mode :Client VTP Domain Name :corp VTP Pruning Mode :Disabled VTP V2 Mode :Disabled VTP Traps Generation :Disabled MD5 digest :0x22 0xF3 0x1A Configuration last modified by 172.18.22.15 at 5-28-03 1t:53:20 What commands must be issued on this switch to add VLAN 50 to the database?（）

多项选择题 There are 2 switches in the Testking LAN, with no routers. Ports 1, 2 & 3 are assigned to VLAN 1 in switch 1 and 2 and ports 4, 5 & 6 are assigned to VLAN 2 in both switches. These two switches are connected together via a trunked link. Which of the conditions below would verify trunk and VLAN operation?（）

单项选择题 A TestKing.com technician is troubleshooting connectivity problems between two routers that are directly connected through the serial line. The technician notices that the serial line is up but cannot see any neighbors displayed in the output of the show cdp neighbors command. In which OSI layer is the problem most likely occurring?（）