Cisco Updated 100-490 Exam Questions and Answers by sahib

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 like shutdown. 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.

Router

The AUX (Auxiliary) port on a router is used for dial-in access for CLI (Command Line Interface) management purposes. It is typically connected to a modem and allows an administrator to dial into the router’s CLI for remote management. This port is not used for passing normal network traffic, which differentiates it from other ports like Fast Ethernet or Gigabit Ethernet that handle regular data flow. The AUX port is specifically designed as a backup async port for management access1.

IPv6 addresses are 128 bits in length and are written as eight groups of four hexadecimal digits. Each group is separated from the others by colons (:). The correct notation for IPv6 addresses allows for the omission of leading zeros within each block of four hexadecimal digits and the use of double colons (::) to represent consecutive blocks of zeros. However, the double colons can only be used once in an address to ensure proper expansion to the full 128 bits. Option B is the only choice that correctly represents a full IPv6 address without any abbreviation. Options A and C use double colons incorrectly, and option D represents a prefix length rather than a full address. References := The information is based on standard IPv6 address notation practices, which include the representation of addresses in hexadecimal format and the rules for abbreviating zeros1

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