100-490 Practice Exam Questions and Answers

A Wide Area Network (WAN) connection typically involves several components that work together to enable data communication over large distances. Two key components of a WAN connection are:

• CSU/DSU (Channel Service Unit/Data Service Unit): This device acts as a gateway between the local area network (LAN) and the WAN. It converts the digital signals used in the LAN to the signals used in the WAN, which are often analog12.
• Router: A router is used to connect multiple networks together and direct data traffic. In the context of a WAN, routers are responsible for determining the best path for data to travel across the network12.

References := Spiceworks, Cisco

IPv4 addresses consist of four octets, each ranging from 0 to 255. The addresses are used to uniquely identify devices on a network.

• A.  

  255.255.255.255is reserved for broadcast messages to all hosts on the local network, so it cannot be assigned to a single host.

• B.  

  10.1.1.20falls within the range of private IP addresses (10.0.0.0 to 10.255.255.255) and can be assigned to a host within a private network.

• C.  

  0.0.0.0is used to denote an unknown or non-applicable target address, often used as a default route, and cannot be assigned to a host.

• D.  

  192.168.10.15is also within the range of private IP addresses (192.168.0.0 to 192.168.255.255) and can be assigned to a host within a private network.

• E.  

  292.10.3.4is not a valid IPv4 address because the first octet exceeds the maximum value of 255.

References:=

• IPv4 Addressing
• Valid IP Address
• IP Address Validation

While the initial answers focused on the most common causes, here's why the other options could also contribute to an interface being stuck in the "up/down" state:

• A.  

  Speed or Duplex Mismatch:Devices on either end of an Ethernet connection need to use compatible speed (e.g., 100 Mbps, 1 Gbps) and duplex (full-duplex or half-duplex) settings. Mismatches can prevent the line protocol from coming up even if the physical link is established.

• B.  

  Layer 2 Mismatch in Encapsulation Type:Some protocols used on Ethernet networks, like ISL and 802.1Q, have specific encapsulation requirements. If devices on each end aren't using the same encapsulation type, the line protocol will likely remain down.

• C.  

  The Ethernet Interface Has Been Manually Disabled:Correct! Administrators can put an interface in a shutdown state using commands likeshutdown. This brings down the line protocol even if the physical connection is good.

• D.  

  Keepalives Are Not Being Received by the Local Device:While less likely to be the sole cause, issues with keepalive mechanisms used in some routing protocols could potentially lead to the line protocol going down. If the local device expects keepalives and doesn't receive them, it might assume a connectivity problem and affect the interface status.

• E.  

  The Ethernet Cable Might Not Be Attached Properly:While a disconnected or faulty cable would usually make the interface down/down, it's possible in some scenarios for a partially connected or damaged cable to result in a link being detected (Layer 1 up) but with errors preventing the line protocol (Layer 2) from initializing.

Troubleshooting network issues often involves considering multiple factors and testing different possibilities. The "up/down" status gives important clues but might have several potential root causes.