Pass the Juniper JNCIA JN0-105 Questions and answers with CertsForce

Layer 2 network switches are crucial components in local area networks (LANs), providing multiple functions for data packet forwarding and network segmentation. One inherent characteristic of switches is their susceptibility to traffic loops, especially in networks with redundant paths. Without proper loop prevention protocols like Spanning Tree Protocol (STP), loops can cause broadcast storms and network instability. Additionally, switches inherently flood broadcast traffic to all ports within the broadcast domain, except the port on which the broadcast was received. This is because broadcast frames are meant to be delivered to all devices within the VLAN, and the switch ensures this by flooding these frames to all ports in the VLAN, except the source port.

The request system zeroize media command on a Junos device securely erases all data, including configuration and log files, and resets the device to its factory default settings. This command is used when redeploying a device to ensure no residual data remains from its previous deployment. It's a comprehensive and secure way to clear all configurations and data, making the device as if it were new. The other commands listed do not perform a full reset to factory defaults; for example, show system storage displays storage information, and request system storage cleanup offers to delete unnecessary files without resetting the device to factory settings.

The firewall filter configuration in the exhibit specifies a filter with two terms. Term 1 matches traffic from the source address 10.0.0.0/8 and has two actions: 'log' and 'next term'. The 'log' action will record the match to a log file, and 'next term' indicates that the firewall should evaluate the next term after logging. There is no explicit action such as 'accept' or 'reject' in term 1, so by default, the traffic will be accepted unless subsequently rejected by another term.

Term 2 has the action 'reject', which discards packets that reach this term. Since there is no 'from' condition in term 2, it acts as a default rule for all traffic not matched by term 1.

Because the traffic sourced from 10.0.0.0/8 matches term 1 and there is no reject action in that term, it will be logged and then accepted by the firewall filter. There is no subsequent term that rejects this specific traffic, so the action from term 2 does not apply to it.

After increasing the MTU size of an interface and committing the configuration, the command to verify the applied MTU change is D, "show interfaces ge-0/0/0." This command displays detailed information about the interface, including the current MTU size, making it the best choice for verifying the applied changes.

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/CD.

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.”

The request system configuration rescue save command in Junos OS saves the most recently committed configuration as the rescue configuration. This rescue configuration can be used to recover the device if future configurations cause issues. It ensures there is a stable, known-good configuration to fall back on, which is crucial in network management and troubleshooting.

To recover the root password on a Junos router without losing the configuration, you should (A) enter and commit the new root password once you have gained access to the system, (D) hit the space bar to interrupt the boot process and enter recovery mode when prompted during the boot process, and (E) use a console connection to reboot the device and access the bootloader prompt. These steps allow you to reset the root password while preserving the existing configuration.

Two physical interface properties in Junos OS include the MAC address (A) and the Maximum Transmission Unit (MTU) size (D). The MAC address is a hardware identifier for the network interface, while the MTU size determines the largest packet size that the interface can transmit without needing to fragment the packet.

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.

The exhibit shows a ping test being executed from router R2 to the IP address 10.23.0.3. Since the ping command is issued on R2 and we see successful replies from 10.23.0.3, it means the source of the ping must be an interface on R2. Given the network diagram and the IP address scheme, the source IP address of the ping is on the interface ge-0/0/2 of R2, which is in the subnet 10.23.0.0/24. The only logical IP address for R2's interface in this subnet, based on standard networking practices and the given options, would be 10.23.0.2. The other addresses provided in the options belong to different subnets or are the destination of the ping itself.