JN0-105 Questions and Answers

In Junos OS, to navigate from operational mode to configuration mode, you can use either the edit or configure command. Both commands move the CLI from operational mode, where you can view the state of the device, to configuration mode, where you can make changes to the device's configuration.

In Juniper Networks devices, when the factory default configuration is loaded, the first step before committing any configuration is to set up root authentication. This is crucial because it secures the device by ensuring that only authorized users have administrative access. Without setting up a root password, the device will not allow any commit operations, which is a safety measure to prevent unauthorized access. This requirement emphasizes the importance Juniper places on security right from the initial setup of the device.

The Packet Forwarding Engine (PFE) is an integral component of Juniper Networks devices, responsible for the data plane operations. The data plane, also known as the forwarding plane, is where the actual processing and forwarding of packets occur based on the routing and forwarding tables. The PFE executes the forwarding decisions made by the Routing Engine (RE), handling all packet transmissions, including routing, filtering, and switching packets towards their destination. This contrasts with the control plane operations handled by the RE, which involve routing table maintenance, system management, and control protocol processing.

Referring to the firewall filter configuration in the exhibit, when a packet matches the specified term limit-icmp, two actions are defined in the then statement: count count-icmp and discard. The count count-icmp action means that each time a packet matches this term, a counter named count-icmp will be incremented, providing a tally of how many packets have matched the term. The discard action means that the packet will be dropped and not forwarded through the device. This effectively prevents the packet from reaching its intended destination. There is no action specified that would cause an ICMP destination unreachable message to be returned, nor is there any action that would allow the packet to be forwarded.

The Routing Protocol Daemon (rpd) in Junos OS is responsible for maintaining routing protocols and tables. It handles all routing information, including the calculation of routes and the population of the routing table, making it crucial for dynamic routing operations.

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.

The Routing Engine (RE) in Junos OS has several critical functions, including processing all management traffic (A) and running the Junos operating system (B). The RE handles system management tasks, user interfaces, system services, and routing protocol processes. It does not directly process transit traffic or evaluate firewall filters for transit traffic, as these tasks are handled by the Packet Forwarding Engine (PFE).

When creating a new policy to accept and redistribute routes into your Interior Gateway Protocol (IGP), the route-filter match criteria is used to identify the route prefixes to select. The route-filter statement specifies which prefixes should be matched in a policy. This allows for precise control over which routes are accepted and redistributed, facilitating efficient and secure routing policies within the network.

References:

"show | display set | match ge-0/0/2" indicating command examples and match criteria from Useful Juniper Commands.txt​​.

Juniper official documentation: Routing Policy and Firewall Filters Configuration Guide.

Junos OS supports only 1 rescue configuration file on a device. This rescue configuration is a safeguard feature that allows network administrators to revert to a known good configuration in case of a configuration error or issue, ensuring network stability.

In Junos OS, each device supports only one rescue configuration file. The rescue configuration is a specific configuration that can be saved and later retrieved if needed. This is used as a fallback configuration that you know works and can be applied in case of an emergency or if the current configuration has issues.

The Routing Engine (RE) in Juniper Networks devices plays a pivotal role in the control plane, handling tasks that are critical for the operation and management of the network. One of its key functions is processing management traffic, which includes user commands, system configuration, and monitoring operations. The RE also maintains routing tables, which are essential for network routing decisions. These tables contain network topology information and routing paths, which the RE uses to update the Packet Forwarding Engine (PFE) so that it can forward packets appropriately. The RE does not forward transit traffic or process Class of Service (CoS) marked traffic, as these tasks are handled by the PFE.

The forwarding table in a network device requires specific information to efficiently forward traffic toward its destination. This includes the next hop IP address, which indicates the next router or device in the path to the destination. The outgoing interface name identifies the physical or logical interface through which the packet should be sent to reach the next hop. Lastly, the next hop MAC address is crucial for Layer 2 forwarding decisions, allowing the device to encapsulate the IP packet in a frame that can be understood by Ethernet or other Layer 2 protocols. OSPF metric values and BGP local preference values are used in the routing decision process to select the best path and populate the forwarding table but are not directly used by the forwarding table to forward traffic.

Class of Service (CoS) in Junos OS provides tools for managing traffic congestion and ensuring that latency-sensitive traffic is given priority over less time-critical data. By implementing CoS, network administrators can classify traffic into different priority levels, apply scheduling policies to ensure that high-priority traffic is transmitted first, and use congestion management techniques such as queue buffers and drop profiles. This helps in maintaining the quality of service for critical applications, especially during periods of high network congestion. However, CoS does not eliminate congestion entirely nor does it inherently make the network faster; it provides a mechanism for better managing and controlling traffic flows according to their importance and time sensitivity.

To advertise a default static route into OSPF on router R1, a routing policy should be configured. This policy would typically include a statement to match the default route (0.0.0.0/0) and then apply an action to set the route as an OSPF external type, which would then be redistributed into the OSPF domain. The routing policy is a set of conditions and actions that determine how routes are imported into or exported from the routing table and how routes are shared between routing instances or routing protocols. After defining the policy, it must be applied to OSPF under the export section of the OSPF configuration on R1. This process will allow R1 to announce the default route to other OSPF routers in the network, which then can use it as a gateway of last resort to reach the Internet or other networks not explicitly known to the OSPF domain.

In the OSI model, the Data Link Layer is responsible for node-to-node delivery of data. It frames the packets received from the Network Layer and prepares them for physical transmission. The Protocol Data Unit (PDU) for the Data Link Layer is called a "frame." Frames encapsulate the network layer packets, adding a header and a trailer that include the hardware addresses of the source and destination, among other things, facilitating the data link layer services like frame synchronization, flow control, and error checking.

The show | compare command in Junos OS is used to display the differences between the candidate configuration and the active configuration. If no output is shown when you issue this command, it means that there are no changes between the candidate configuration and the active configuration. This indicates that the candidate configuration is identical to the active configuration, and thus no differences are displayed.

In Junos OS, the prompt employee@R1> indicates the current context of the user interface. The 'R1' part of the prompt signifies the hostname of the device, which in this case is 'R1'. The absence of a '#' symbol at the end of the prompt suggests that the user is in operational mode, as opposed to configuration mode which is indicated by a prompt ending in '#'. Operational mode allows users to view the status of the device and execute operational commands, but does not allow for configuration changes.

The Network Time Protocol (NTP) is designed to synchronize the clocks of computers over a network. Configuring NTP on a Junos device ensures that its clock is set accurately, which is crucial for logging, troubleshooting, and maintaining the integrity of time-sensitive operations and security protocols. NTP allows devices to use a hierarchy of time sources, from primary servers synchronized to a reference clock (such as an atomic clock or GPS time) to secondary servers that distribute the time to other devices on the network.

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.

To convert the decimal number 7 to binary, the correct representation is 00000111 (C). In binary, 7 is represented as 1+2+4 (2^0 + 2^1 + 2^2), which corresponds to the last three digits being 1 in the binary format, with leading zeros added for clarity.

When you enter ? at the command-line prompt in Junos OS, the system provides assistance in two significant ways. Firstly, it lists the available commands and options that can be used at the current point in the command hierarchy, aiding users in understanding what commands they can execute next. Secondly, it displays summary information about those commands and options, providing brief descriptions or additional context that can help users understand the function of each command or option. This feature is particularly useful for learning the command structure or for quick reference when specific command syntax is forgotten.

RADIUS, which stands for Remote Authentication Dial-In User Service, provides authentication services for users trying to access a network. It is a networking protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management for users who connect and use a network service.

In Junos OS, remote access to the device's CLI is commonly facilitated through Secure Shell (SSH), a protocol providing secure command-line access over an insecure network. The given exhibit indicates an attempt to set a root authentication password but does not show configuration for enabling remote access services. To enable SSH, which is not shown in the configuration snippet, you need to configure the device to accept SSH connections. This is done by enabling the SSH service within the system services hierarchy of the configuration. The correct command to add to the existing configuration for enabling remote CLI access via SSH is set system services ssh. This command activates the SSH service, allowing secure remote logins to the device.

In Junos OS, when two entries for the same destination exist in the routing table, the route with the lowest preference number is selected as the active route. This preference number, also known as the route preference or administrative distance, is used to prioritize routes received from different routing protocols.

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.

In Junos OS, the # prompt indicates that you are in configuration mode. This mode is used for making changes to the configuration of the device.