At which layer of the OSI model dose PPP perform?（）……

单项选择题Which command is used to display the collection of OSPF link states?（）

A. show ip ospf lsa database
B. show ip ospf link-state
C. show ip ospf neighbors
D. show ip ospf database

单项选择题When you are troubleshooting an ACL issue on a router,which command can help you to verify which interfaces are affected by the ACL?（）

A. show ip access-list
B. show access-list
C. list ip interface
D. show interface
E. show ip interface

单项选择题Three switches are connected to one anther via trunk ports.Assuming the default switch configuration,which switch is elected as the root bridge for the spanning-tree instance of vlan 1?（）

A. the switch with the lowest MAC address
B. the switch with the higest MAC address
C. the switch witch the higest IP address
D. the switch with the lowest IP address

单项选择题What is the purpose of the cisco Vlan Trunking protocol?（）

A. to provide a mechanism to dynamically assign vlan membership to switch ports
B. to allow traffic to be carried from multiple vlans over a single link between switches
C. to allow native vlan information to be carried over a trunk link
D. to provide a mechanism to manually assign vlan membership to switch ports
E. to allow for managing the additions,deletions,and changes of vlans between switchs

单项选择题Which cisco ios command can help to determine the timing of various debug events,relative to each other,when you are debugging a complicated router issue?（）

A. service timestamps debug datetime msec
B. show clock detail
C. clock calendar-valid
D. service timestamps log datetime msec