JN0-105 Questions and Answers

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.

The show route table inet6.0 command displays all IPv6 routes in the default routing instance. In Junos OS, the routing table for IPv6 addresses is referred to as inet6.0, whereas inet.0 is used for IPv4 unicast routes. The other options do not correspond to the correct IPv6 routing table.

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.

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 the exhibit shown, the highlighted number next to the route type (Static) within the square brackets indicates the route preference, also known as the administrative distance. In Junos, the route preference is a value that determines the priority of the route source. Lower numbers indicate a higher priority when the routing table is being calculated. The route preference is used to select the best route when multiple paths to the same destination exist from different routing sources. The number 5 is unusually low for a static route by default, suggesting it has been manually configured to override other route types.

When configuring the system-related settings for the current date and time on a Junos device, especially for a specific time zone like America/Los_Angeles, and the time does not automatically adjust, two effective actions can be taken. Firstly, setting the date and time manually allows for immediate correction of the system clock. This can be done via the CLI with the appropriate set date and time command. Secondly, configuring the device to use an NTP server can provide ongoing synchronization with an accurate time source, ensuring that the device maintains the correct time and date automatically in the future, even in the case of restarts or minor drifts in the internal clock.

In the scenario where the system authentication order is set to "tacplus radius password," the correct statement is (B). If the TACACS+ and RADIUS servers are unreachable or fail to respond, the system will fall back to using password authentication. This ensures that users can still authenticate using locally stored passwords if external authentication servers are unavailable.

Exception traffic refers to packets that the Packet Forwarding Engine (PFE) cannot process normally and must be forwarded to the Routing Engine (RE) for further processing. This includes packets destined for the router itself or packets needing special handling that the PFE cannot provide. To protect the RE from being overwhelmed by such traffic, which could potentially impact the router's control plane functions, exception traffic is rate-limited. This means that there's a threshold to how much exception traffic can be sent to the RE, ensuring that the router's critical management and control functions remain stable and responsive even during high traffic volumes or attacks.

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.

In the context of VLANs (Virtual Local Area Networks) on a Juniper switch, the numerical values assigned to each VLAN, such as those for Prod, Test, and Dev, are known as VLAN tags. These tags are part of the 802.1Q VLAN standard, which allows multiple VLANs to coexist on a single physical network. Each tag uniquely identifies the VLAN to which a frame belongs, enabling the switch to segregate and manage traffic based on VLAN membership. This tagging mechanism allows for efficient traffic separation and management, ensuring that devices within one VLAN do not receive traffic intended for another, thus maintaining network security and efficiency.

Junos OS supports multiple methods for automatically archiving configurations upon commit. Two of the supported methods are SCP (Secure Copy Protocol) and RCP (Remote Copy Protocol). These methods can be configured to save the configuration files to a remote server automatically whenever a commit is made.

For the users in the 10.1.1.0/24 subnet and the server in the 10.1.2.0/24 subnet to communicate with each other, they need to route packets through the router that connects these two subnets. Each user and the server need to have their default gateway set to the IP address of the router interface on their respective subnet (.254). This ensures that packets destined for other subnets are sent to the router, which then routes them to the correct destination subnet.

The TCP three-way handshake establishes a reliable connection between two hosts. During this process:

SYN: The client sends a TCP segment with the SYN flag set, including an initial sequence number (ISN) and port information.

SYN-ACK: The server responds with a SYN-ACK, which contains its own sequence number and acknowledgment of the client’s ISN.

ACK: The client replies with an ACK, confirming receipt of the server’s ISN.

Thus, port numbers (to identify the application endpoints) and sequence numbers (to ensure ordered and reliable data transfer) are exchanged.

Interfaces and application names are not exchanged during this process.

From Junos OS Fundamentals / TCP Concepts:

“The TCP three-way handshake establishes a reliable session by exchanging port numbers and sequence numbers between peers. This process synchronizes both sides before data transmission begins.”

In the given telnet command, "telnet 10.10.10.1 source 192.168.100.1," the destination address of the telnet session is 10.10.10.1, and the source address of the session is specified as 192.168.100.1, making C and D the correct answers. This command instructs the telnet client to use the specified source IP address when establishing the connection to the destination.

Firewall filters in Junos OS are stateless, meaning they process each packet individually without regard to the state of a connection or sequence of packets. These filters can match various packet attributes, including those at Layer 4, such as TCP and UDP port numbers. This allows for granular control over traffic based on the type of service or application. Unlike stateless filters, stateful firewalls keep track of the state of active connections and make decisions based on the context of the traffic flow, which is not a capability of Junos firewall filters. Additionally, Junos firewall filters primarily operate up to Layer 4 and do not natively inspect Layer 7 parameters, which involve application-level data.

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).

Junos OS supports several external authentication methods for administrative access, with TACACS+ (Terminal Access Controller Access-Control System Plus) and RADIUS (Remote Authentication Dial-In User Service) being among the most commonly used. Both TACACS+ and RADIUS are protocols that allow network devices to communicate with a central authentication server, enabling centralized control over user authentication and authorization. This centralization simplifies the management of user credentials and access policies, especially in larger networks with multiple devices.

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.

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.

The clear log ospf-trace command on a Juniper Networks router is used specifically to manage the contents of the log file named ospf-trace. Executing this command clears or deletes the existing data within the ospf-trace log file but does not stop the logging process. The router continues to log new OSPF-related events and data into this file after the command is executed. This functionality is crucial for troubleshooting and monitoring the OSPF (Open Shortest Path First) protocol's operation by allowing network administrators to remove old or irrelevant log data while continuously capturing new events without interruption.

In the Junos CLI, the pipe character | is used as a filter operator to refine command output. This operator can be combined with various filtering commands like match, except, count, etc., to display only the relevant portions of the command output. For example, using | match <pattern> filters the output to show only the lines that contain the specified pattern, making it easier to find specific information within extensive command output. This functionality is especially useful in managing and troubleshooting complex configurations and network states, allowing for more efficient analysis of the device's operational status and configuration details.

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.

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.

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.

In Juniper firewall filter configurations, "discard" and "accept" are two valid terminating actions for a term within a filter. The "discard" action drops the packet, preventing it from reaching its intended destination, while the "accept" action allows the packet to pass through the filter, proceeding to its next hop or destination. "Count" is a non-terminating action that increments a counter every time a packet matches the term but does not inherently determine the packet's fate. "Next term" directs the evaluation to proceed to the next term in the filter for further processing, also a non-terminating action.

In Junos OS, when a user issues the configure exclusive command, it locks the candidate configuration for that user, preventing other users from making concurrent configuration changes. This exclusive lock ensures that configuration changes are managed in a controlled manner, reducing the risk of conflicting changes. As a result, while one user is in exclusive configuration mode, other users are prevented from entering configuration mode until the lock is released, either by the user committing the changes or exiting configuration mode.

Junos OS selects routes based on the route preference (also known as administrative distance). Static routes typically have a lower route preference than OSPF routes, meaning they are more preferred. Since the static route to 192.168.36.1/32 is shown with a preference of 5, it will be selected over the OSPF route for packet forwarding, assuming no other factors such as route filters or policies affect the routing decision.