JN0-105 Practice Questions

CSMA/CD is the access method used in classic Ethernet (half-duplex). Its main functions:

Carrier Sense: A device listens to the medium to check if another device is transmitting before sending (avoiding collisions).

Collision Detection: If two devices transmit at the same time, they detect the collision, stop, and wait a random backoff period before retrying.

Devices can either transmit or receive at a given time (half-duplex), not both simultaneously.

Thus, correct answers:

✔ A – Listen before transmit.

✔ B – Devices can either transmit or receive.

Options C and D are incorrect:

CSMA/CD is a half-duplex protocol, not full-duplex.

Full-duplex eliminates collisions and no longer uses CSMA/C

D.  

From JNCIA-Junos Study Guide:

“CSMA/CD requires that devices sense the wire before transmitting. Devices can either transmit or receive, but not both at the same time.”

MAC (Media Access Control) addresses are unique identifiers assigned to network interfaces for communications at the data link layer of a network segment. MAC addresses are used to identify the physical hardware on a network. In the context of Ethernet switches, the destination MAC address in incoming frames is used to determine the appropriate output port for forwarding the frame towards its final destination. The switch does not change the destination MAC address; it uses the MAC address to make forwarding decisions within the local network segment.

Traceoptions in Junos OS are used for detailed debugging and troubleshooting of protocols and processes within the system. They are not enabled by default due to the potential performance impact and volume of data generated. Instead, traceoptions are enabled through specific configuration settings under the relevant protocol or process hierarchy. This allows administrators to target their troubleshooting efforts and control the scope of logging. By default, the output generated by traceoptions is stored in files located in the /var/log directory, with the file name typically specified in the traceoptions configuration. This structured approach to logging and debugging helps in diagnosing complex issues without overwhelming the system or the administrator with irrelevant data.

In Junos OS routing policy evaluation, "next policy" (A) and "next term" (C) are common actions that affect the flow of policy evaluation. "Next policy" directs the evaluation to the next policy in the sequence, whereas "next term" moves the evaluation to the next term within the current policy, allowing for granular control over routing decisions.

UDP (User Datagram Protocol) is known for being connectionless (D) and providing best-effort delivery without the reliability mechanisms present in TCP (C). This means that UDP does not establish a connection before sending data and does not guarantee delivery, order, or error checking, making it faster but less reliable than TCP.