Explanation:
The set of commands which would be used to configure the Telnet password to “john” on a Cisco router is:

Router(config)#line vty 0 4 Router(config-line)#login Router(config-line)#password john

The line vty command is used to configure the router to enable Telnet access. By using this command, the router can be configured to accept one or more Telnet sessions.

The login and password parameters are the line configuration commands used to configure the password. The password command specifies the password and the login command instructs the router to require the password. By default, the login parameter is present in the configuration of the VTY lines. Because its presence indicates that a password is required for connecting to the VTY lines, if a password has not been configured on the VTY lines, a connection cannot be made. If an attempt were made to connect to the VTY line with the login parameter in effect and no password present, the following error message would be generated:

Router2# telnet 10.3.1.1
Trying 10.3.1.1Open

Password Required, but none set
[Connection to 10.3.1.1 closed by foreign host]
Router2#

Explanation:
The output given in the question is produced with the show interfaces command. This command is used to view the statistics for the configured interfaces on the router. From the sample output, we can determine the following facts:
The interface has not been enabled, as indicated by the first line Serial0/0/0 is administratively down. It is not ready to for to forward packets. To enable it, the no shutdown command should be entered.
Line 3 shows that the subnet mask is 255.255.255.0.
Line 3 shows that the IP address is 134.108.28.8, a public IP address. Line 6 shows that the encapsulation is HDLC, which is the default.
The interface is NOT connected to a LAN, because it is a serial interface.

Two fields worth mentioning in the output of the show interfaces command are the no buffer and the ignored fields. The ignored field shows the number of received packets ignored by the interface because the interface hardware ran low on internal buffers. The no buffer field shows the number of received packets discarded because there was no buffer space in the main system. When either of these two counters begins to increment, it could be the result of a broadcast storm.

Explanation:
The switchport mode trunk command is used on the Cisco Catalyst 2950 switch to configure a port as a VLAN trunk port. The syntax of the command is as follows:

Switch(config-if)# switchport mode trunk

Trunk links are required between devices in any situation where traffic from multiple VLANs will traverse the link. This is also true when using VTP on the switches
and in that case, even if inter-VLAN routing is not required. For example, if two switches in a VTP domain are connected together via an access link with no router present, then when you create a new VLAN on one of the switches, it will NOT be learned by the other switch.

When you configure a trunk link, there are two choices for encapsulation: 802.1q, which is the industry standard, and ISL, which is Cisco proprietary and will only work when both ends are Cisco equipment. Both protocols perform a crucial role in inter-VLAN routing by tagging packets with the VLAN to which the packets belong.

Explanation:
For all switches in a VTP domain, the VTP version, VTP password, and VTP domain name must be the same. Moreover, switches that will share VLAN information must be operating in VTP server mode, must be using the same VLAN tagging method (either 802.1q or ISL), and must be connected with trunk links.

Many of these settings can be verified by using the show vtp status command. By viewing the output of the command on two switches that are not sharing information, inconsistencies that prevent the sharing of VLAN information can be identified.

Explanation:
Only the router requires the ipv6 unicast-routing command. The command ipv6 unicast-routing enables the routing of IPv6 packets on a router. It is not required when you are simply configuring interfaces on devices that participate in IPv6.

A Layer 2 switch can have an IPv6 address applied to its management interface and to any VLAN interfaces. However, because the switch does no routing, it does not require the ipv6 unicast-routing command.

An adaptive security appliance (ASA) can also have IPv6 addresses applied to its interfaces and can route both IPv6 and IPv4 traffic. However, it does not require the ipv6 unicast-routing command.
A wireless access point differs from a wireless router in that it operates as a switch or hub and does no routing. Therefore, it does not require this command.

Explanation:
A late collision is defined as any collision that occurs after the first 512 bits (or 64th byte) of the frame have been transmitted. The usual possible causes are full-duplex/half-duplex mismatch, exceeded Ethernet cable length limits, or defective hardware such as incorrect cabling, non-compliant number of hubs in the network, or a bad NIC. Late collisions should never occur in a properly designed Ethernet network. They usually occur when Ethernet cables are too long or when there are too many repeaters in the network.

Explanation:
Indicates that the cyclic redundancy checksum generated by the originating LAN station or far-end device does not match the checksum calculated from the data received. On a LAN, this usually indicates noise or transmission problems on the LAN interface or the LAN bus itself. A high number of CRCs is usually the result of collisions or a station transmitting bad data.

Explanation:
If the destination MAC address is not in the CAM table (unknown destination MAC address), the switch sends the frame out all other ports that are in the same VLAN as the received frame. This is called flooding. It does not flood the frame out the same port on which the frame was received.

Explanation:
172.28.0.0/16 is a private IP address range.