Juniper JN0-351 Exam Dumps & Practice Test Questions
Question 1:
In Rapid Spanning Tree Protocol (RSTP), various port roles are designated to manage loop-free topologies. Some of these port roles place their interfaces into the discarding state, either temporarily or indefinitely, to prevent loops.
Which three port types can exist in the discarding state under RSTP? (Select three)
A. Port serving as the Root Path to the root bridge
B. Port acting as a backup for another designated port on the same segment
C. Alternate port offering a secondary path to the root bridge
D. Interface administratively shut down or inactive
E. Port assigned to transmit traffic on a segment
Answer: B, C, D
Explanation:
In Rapid Spanning Tree Protocol (RSTP), the discarding state is used to prevent network loops and is primarily used to place certain types of ports into a non-forwarding mode, meaning they do not participate in the data traffic transmission. This helps to maintain a loop-free topology while allowing RSTP to quickly respond to changes in the network topology. Here’s how each port role relates to the discarding state:
B. Port acting as a backup for another designated port on the same segment:
A Backup Port is placed into the discarding state in RSTP. This port serves as a secondary path in case the designated port fails, but it does not forward traffic while the primary port is active. This helps to prevent loops in the network.C. Alternate port offering a secondary path to the root bridge:
An Alternate Port is another port that provides an alternative path to the root bridge. However, it is not used unless the primary port fails. In RSTP, alternate ports are placed in the discarding state until they are needed (i.e., if the primary path goes down). These ports help ensure that traffic can be rerouted quickly in the case of a failure but are not actively forwarding under normal conditions.D. Interface administratively shut down or inactive:
Ports that are administratively shut down or otherwise inactive (such as due to a configuration setting) are placed into the discarding state because they are not used for forwarding traffic. These ports are essentially disabled and are not part of the active forwarding path in the network.
Why the other options are not correct:
A. Port serving as the Root Path to the root bridge:
The Root Port is the port on a non-root bridge that has the best path to the root bridge. Root ports are always in a forwarding state, not discarding, because they are actively used for traffic transmission towards the root bridge.E. Port assigned to transmit traffic on a segment:
Ports that are actively transmitting traffic, such as Designated Ports, are in a forwarding state in RSTP. They are used to send and receive data on the network segment. They do not enter the discarding state unless there is a topology change that requires it.
In conclusion, the discaring state in RSTP applies to Backup Ports, Alternate Ports, and administratively shut down ports because they are either standby paths or inactive ports that do not actively participate in forwarding traffic unless needed.
Question 2:
Within an OSPF multi-access network such as Ethernet, the Designated Router (DR) is elected to minimize protocol traffic. If two routers with identical, highest OSPF priority values start the election process simultaneously, a tie-breaking mechanism is used.
After matching OSPF priority values, what is the next factor OSPF uses to choose the Designated Router?
A. Router with the numerically smallest router ID
B. Router with the numerically largest router ID
C. A new election process is initiated
D. Router with the highest hardware (MAC) address
Answer: B. Router with the numerically largest router ID
Explanation:
In OSPF (Open Shortest Path First), when a Designated Router (DR) needs to be elected on a multi-access network (like Ethernet), OSPF priority is the first factor used in the election process. If multiple routers have the same highest OSPF priority value, a tie-breaking mechanism is invoked to determine which router becomes the DR.
The tie-breaking mechanism is as follows:
If the OSPF priority values are identical, the next factor that OSPF uses is the Router ID.
The router with the numerically largest router ID will be selected as the Designated Router (DR).
The Router ID in OSPF is typically based on the highest IP address of a router’s interfaces, but it could also be manually configured.
Why the other options are incorrect:
A. Router with the numerically smallest router ID:
This would be incorrect because, in the event of a tie in OSPF priority, the router with the largest router ID is selected, not the smallest.C. A new election process is initiated:
This is not how OSPF resolves ties. OSPF does not re-initiate an election based on tied priority values; instead, it uses the router ID to resolve the conflict.D. Router with the highest hardware (MAC) address:
OSPF does not consider the MAC address for DR elections; it only uses OSPF priority and router IDs. MAC addresses are part of the underlying Ethernet protocol, not the OSPF election process.
Thus, the correct answer is B. Router with the numerically largest router ID.
Question 3:
On Juniper EX Series switches, Redundant Trunk Groups (RTGs) are used to maintain Layer 2 redundancy. RTGs allow one uplink to be active while another stands by to ensure fault tolerance.
Which two statements correctly describe how RTGs function on Juniper EX switches?
A. Traffic is load-balanced equally between both trunk ports
B. If the active link fails, the standby link automatically takes over without user intervention
C. Layer 2 control traffic such as BPDUs is permitted to pass over the standby interface
D. Both trunk ports must be linked to the same upstream switch or aggregation point
Correct answers: B. If the active link fails, the standby link automatically takes over without user intervention and D. Both trunk ports must be linked to the same upstream switch or aggregation point
Explanation:
B. If the active link fails, the standby link automatically takes over without user intervention:
This is correct. Redundant Trunk Groups (RTGs) provide failover capability for Layer 2 links. If the active link fails, the standby link automatically takes over to ensure continuous service without requiring manual intervention. This is one of the primary features of RTGs to provide fault tolerance.
D. Both trunk ports must be linked to the same upstream switch or aggregation point:
This is also correct. RTGs are used to provide redundancy between two trunk ports on the switch, and both of these ports must be connected to the same upstream switch or aggregation point. The two links do not provide redundancy across different switches but instead ensure high availability on the same upstream device.
Why the other options are incorrect:
A. Traffic is load-balanced equally between both trunk ports:
This is incorrect. RTGs do not perform load balancing between the active and standby ports. Only the active port carries traffic under normal circumstances, while the standby port remains idle unless the active port fails. There is no load balancing between the two ports, so only one link is active at a time.
C. Layer 2 control traffic such as BPDUs is permitted to pass over the standby interface:
This is incorrect. The standby port in an RTG setup does not forward data traffic or Layer 2 control traffic (such as BPDUs) unless it becomes the active port. The standby port is simply a backup and does not participate in traffic forwarding under normal operation.
Thus, the correct answers are B and D.
Question 4:
Which two methods are used in BGP to avoid routing loops across AS boundaries?
A. When advertising routes, an eBGP router adds its own AS number to the AS_PATH
B. An eBGP router allows routes with its own AS number in the AS_PATH to maintain bidirectional flow
C. An eBGP router will reject routes that include its own AS number in the AS_PATH
D. An eBGP router may repeat its AS number multiple times in the AS_PATH to make the route less preferred by others
Correct Answer: C, A
Explanation:
BGP (Border Gateway Protocol) is a path vector protocol that facilitates inter-domain routing between different Autonomous Systems (ASes). One of its primary concerns is preventing routing loops, which can lead to network instability. BGP uses several mechanisms to avoid such loops, particularly when exchanging routing information between different ASes.
The AS_PATH attribute is a crucial mechanism for preventing routing loops in BGP. This attribute lists the ASes that a route has traversed, essentially keeping a record of all the ASes involved in the route's path. By examining this attribute, BGP routers can detect and reject any route that would cause a loop.
Option A: "When advertising routes, an eBGP router adds its own AS number to the AS_PATH"
This option is correct because when an eBGP router advertises a route to another AS, it appends its own AS number to the AS_PATH. This allows other routers to see which ASes the route has already passed through. The inclusion of the AS number prevents routing loops by ensuring that an AS will not accept a route that has already passed through it.
Option C: "An eBGP router will reject routes that include its own AS number in the AS_PATH"
This option is also correct because BGP routers, when receiving a route advertisement, will check the AS_PATH. If the router detects its own AS number in the AS_PATH, it knows that the route has already passed through its own AS, which would indicate a potential loop. To prevent this, the router will reject the route and not propagate it further. This is a key mechanism for loop prevention in BGP.
Option B: "An eBGP router allows routes with its own AS number in the AS_PATH to maintain bidirectional flow"
This option is incorrect because BGP explicitly rejects any route that contains its own AS number in the AS_PATH. Allowing such a route would cause routing loops, making the network unstable. Therefore, this behavior is not part of BGP's loop-prevention mechanisms.
Option D: "An eBGP router may repeat its AS number multiple times in the AS_PATH to make the route less preferred by others"
This option is also incorrect. Repeating an AS number multiple times in the AS_PATH would not prevent loops and would only serve to confuse the routing process. BGP does not use multiple repetitions of the same AS number in the AS_PATH as a mechanism for making routes less preferred. Instead, the BGP route selection process uses other metrics, such as local preference or AS path length, to influence the preference of routes.
In summary, BGP uses the AS_PATH attribute to detect and prevent routing loops. The router adds its AS number to the AS_PATH when advertising routes, and it rejects routes containing its own AS number in the AS_PATH to avoid loops. These mechanisms are essential for maintaining stable and loop-free routing in inter-domain routing environments.
Question 5:
Which statement correctly reflects the requirements of an IS-IS NET address?
A. A system ID of all zeroes (0000.0000.0000) designates the router as DIS
B. Every router must have a unique NET address in the IS-IS domain
C. A device can only be configured with a single NET address
D. All routers in the same Level 2 IS-IS area must use identical Area IDs
Correct Answer: B
Explanation:
In IS-IS (Intermediate System to Intermediate System), the NET (Network Entity Title) is a critical identifier used to uniquely address routers in an IS-IS domain, and it plays a vital role in the routing process. The NET address is composed of multiple components, including the Area ID and System ID, which are necessary for identifying and routing between various routers within an IS-IS network. The NET address is used both to identify a router and to ensure proper routing functionality within IS-IS areas and levels.
The format of the NET address is as follows:
The Area ID identifies a particular region of the network.
The System ID is unique to each router within a given area and helps to distinguish different routers.
The Network Entity Title is a concatenation of the Area ID and System ID, forming the full NET address.
Option A: "A system ID of all zeroes (0000.0000.0000) designates the router as DIS"
This option is incorrect. A System ID of all zeroes does not specifically designate a router as the DIS (Designated Intermediate System) in IS-IS. The DIS role is assigned to a router based on a separate election process that takes place in IS-IS networks. The System ID of all zeroes is not used to mark a router as the DIS.
Option B: "Every router must have a unique NET address in the IS-IS domain"
This option is correct. In IS-IS, each router within the network must have a unique NET address to avoid conflicts and ensure proper routing operations. The NET address includes both the Area ID (which defines the routing domain) and the System ID (which identifies individual routers), and this combination must be unique within the IS-IS domain. This uniqueness allows routers to be properly identified and to exchange routing information.
Option C: "A device can only be configured with a single NET address"
This option is incorrect. While a router must have a unique NET address for each Area in which it participates, it is possible for a device to have multiple NET addresses if it belongs to more than one IS-IS area. In such cases, the router can have different NET addresses for each area, as each Area ID in the NET address is specific to the IS-IS area the router is part of.
Option D: "All routers in the same Level 2 IS-IS area must use identical Area IDs"
This option is incorrect. The Area ID in IS-IS is a part of the NET address, but routers in the same Level 2 IS-IS area do not need to have identical Area IDs. The Area ID is shared by routers that belong to the same IS-IS area, but each router has a unique System ID within that area. The area, represented by the Area ID in the NET, defines the scope of routing exchanges but does not need to be identical across routers. The uniqueness of the System ID ensures that the routers are individually identifiable.
In conclusion, Option B is correct because every router in an IS-IS network must have a unique NET address for accurate and conflict-free routing. The NET address combines the Area ID and System ID, and the uniqueness of the System ID within each area ensures proper routing. Other options either misunderstand the role of certain identifiers or present incorrect conditions for IS-IS operation.
Question 6:
What is the default time interval configured on a Juniper EX switch after which an unused MAC address is removed from the MAC table?
A. 1800 seconds (30 minutes)
B. 30 seconds
C. 18000 seconds (300 minutes)
D. 300 seconds (5 minutes)
Correct Answer: A
Explanation:
In networking, switches maintain a MAC address table (also known as a forwarding table) that stores the MAC addresses of devices connected to the switch and associates each MAC address with a specific port. This allows the switch to efficiently forward Ethernet frames to the correct destination. However, when devices become inactive or disconnected, the switch must eventually remove these entries to ensure that the MAC address table doesn't become outdated or too large, which could lead to performance issues.
The MAC aging timer determines the amount of time a MAC address remains in the MAC address table before it is considered stale and removed. This aging process is important because it ensures that the table reflects current network activity. If a device is inactive (i.e., there has been no traffic from its MAC address), its entry will eventually expire and be removed.
For Juniper EX switches, the default MAC aging timer is set to 1800 seconds (30 minutes). This means that if a MAC address is not used for 30 minutes, it will be aged out of the MAC address table. This is a reasonable default for most networks, as it provides a balance between efficiency and the need to keep the table updated with current active MAC addresses.
Option A: "1800 seconds (30 minutes)" is the correct answer because this is the default aging time on Juniper EX switches.
Option B: "30 seconds" is too short a time for a MAC address aging timer. In most networks, 30 seconds would not allow sufficient time for devices to be recognized and allow for normal activity on the network. This is not the default setting for Juniper EX switches.
Option C: "18000 seconds (300 minutes)" represents 5 hours, which is much too long for the aging timer. While it might be suitable for some very stable networks, this is not the default setting for Juniper EX switches, as it would result in outdated information persisting for far too long.
Option D: "300 seconds (5 minutes)" is a shorter aging period than the default. A 5-minute aging time is often used in more dynamic environments, but it is not the default for Juniper EX switches, which typically use the 30-minute aging timer.
In conclusion, the correct default MAC aging timer on a Juniper EX switch is 1800 seconds (30 minutes), which ensures that the MAC address table is refreshed periodically without unnecessarily removing addresses too quickly. This default can be adjusted based on the specific needs of the network, but Option A is the correct answer.
Question 7:
Which two statements describe how generated routes operate in Junos OS?
A. A generated route becomes active only when at least one supporting route exists
B. Generated routes always specify a fixed next-hop address
C. They appear under the static routing category in the routing table
D. Generated routes can be redistributed into dynamic protocols like OSPF and BGP
Correct Answer: A, D
Explanation:
In Junos OS, generated routes are special routes that are created automatically by the system to simplify the routing table and provide summarization or default route capabilities. These routes are not manually configured but instead are based on certain routing conditions or network policies. Understanding how they operate is important for managing routing in Junos-based environments, particularly when trying to optimize and simplify the routing table.
Option A: "A generated route becomes active only when at least one supporting route exists"
This option is correct. In Junos OS, generated routes are often used to summarize or create default routes based on the presence of existing routes. A generated route will only become active if there is a supporting route that meets specific criteria, such as being reachable or valid within the routing table. For example, if the system is generating a default route based on specific conditions, it will only be installed into the routing table if there is a route that supports its creation, such as a valid route for the destination network.
Option B: "Generated routes always specify a fixed next-hop address"
This option is incorrect. Generated routes do not always specify a fixed next-hop address. Instead, generated routes typically act as summary routes or default routes and do not need to specify a specific next-hop address in every case. The next-hop for generated routes can be determined dynamically, depending on the specific routing conditions and how the route is being used. For example, a generated default route may simply direct traffic to a default next-hop without having a fixed value.
Option C: "They appear under the static routing category in the routing table"
This option is incorrect. While generated routes are similar in some ways to static routes because they are manually configured for specific purposes (like route summarization), they do not appear directly under the static routing category in the routing table. Instead, they appear under their own specific category. Generated routes are created based on certain routing policies and are not typically classified as static routes, although they may be similar in function in terms of network design.
Option D: "Generated routes can be redistributed into dynamic protocols like OSPF and BGP"
This option is correct. Generated routes can be redistributed into dynamic routing protocols like OSPF and BGP. This allows the generated route to be shared with other routers in the network, making it possible to include the summarized or default route in the overall network's routing decisions. By redistributing generated routes into dynamic protocols, a network administrator can enable wider use of these routes, making the network more scalable and efficient.
In summary, generated routes in Junos OS are designed to simplify the routing table, support summarization, and provide default route capabilities. They are conditional and active only when supported by valid routes, and they can be redistributed into dynamic routing protocols such as OSPF and BGP.
Question 8:
What is the main responsibility of the Spanning Tree Protocol (STP) within Ethernet-based switch networks?
A. To manage the MAC address learning table on switches
B. To block loops and prevent broadcast storms in a Layer 2 environment
C. To select the shortest IP route across interconnected networks
D. To encapsulate Ethernet traffic for cross-platform delivery
Correct Answer: B
Explanation:
The Spanning Tree Protocol (STP) is a network protocol used primarily in Layer 2 Ethernet networks to prevent loops that can occur due to redundant paths between switches. These loops can cause broadcast storms, network congestion, and instability in the network. STP works by creating a loop-free topology in a network of interconnected switches.
The primary responsibility of STP is to ensure that data frames are delivered across the network without causing a loop, which could otherwise result in infinite data circulation between switches, consuming network bandwidth and creating congestion. It dynamically adjusts the network topology by blocking certain redundant paths, leaving only one active path between any two switches in the network.
Option A: "To manage the MAC address learning table on switches"
This option is incorrect. The MAC address learning table, also known as the MAC address table or forwarding table, is used by switches to keep track of which MAC addresses are associated with which switch ports. While switches do manage this table, STP is not responsible for learning MAC addresses. The MAC address table is built and updated dynamically as frames are received by the switch.
Option B: "To block loops and prevent broadcast storms in a Layer 2 environment"
This option is correct. The main responsibility of STP is to block loops in a Layer 2 environment, which can occur due to redundant paths between switches. By blocking some of these paths (using a process called port blocking), STP ensures that data flows along a single path between switches and prevents network issues such as broadcast storms or frame duplication. This is crucial for maintaining network stability and preventing congestion.
Option C: "To select the shortest IP route across interconnected networks"
This option is incorrect. The Spanning Tree Protocol (STP) operates at Layer 2 (the Data Link layer), not Layer 3 (the Network layer), and it is not involved in IP routing. The selection of the shortest IP route is the responsibility of Layer 3 protocols, such as Routing Information Protocol (RIP), Open Shortest Path First (OSPF), or Border Gateway Protocol (BGP), which are designed to determine the most efficient path for data to travel based on IP addresses.
Option D: "To encapsulate Ethernet traffic for cross-platform delivery"
This option is incorrect. The encapsulation of Ethernet traffic, particularly for cross-platform or inter-network delivery, is not a function of STP. Encapsulation refers to the process of wrapping data in a specific protocol format, such as when Ethernet frames are encapsulated in IP packets or MPLS labels for forwarding across networks. This is typically handled by protocols like IP or MPLS, not STP.
In conclusion, the main responsibility of Spanning Tree Protocol (STP) is to block loops and prevent broadcast storms in a Layer 2 network by maintaining a loop-free topology. This ensures stable and efficient data flow across the network, making Option B the correct answer.
Question 9:
Which two tunnel types are supported across all Junos platforms for traffic encapsulation purposes?
A. Spanning Tree Protocol (STP)
B. Generic Routing Encapsulation (GRE)
C. IP-in-IP encapsulation (IP-IP)
D. IPsec tunnels for encrypted communication
Correct Answer: B, C
Explanation:
Junos OS, developed by Juniper Networks, provides support for a range of tunneling technologies used to encapsulate and transport network traffic securely or efficiently across different parts of a network. These technologies play a critical role in areas like network security, traffic optimization, and interconnecting remote locations.
In particular, the tunneling technologies that are supported across all Junos platforms for encapsulating traffic include Generic Routing Encapsulation (GRE) and IP-in-IP encapsulation (IP-IP). Let’s explore these options in more detail.
Option A: Spanning Tree Protocol (STP)
This option is incorrect because STP (Spanning Tree Protocol) is not a tunneling technology. STP operates at Layer 2 to prevent loops in Ethernet-based networks and does not perform traffic encapsulation. The role of STP is to manage the topology of a network to avoid redundant loops, not to encapsulate traffic between devices.
Option B: Generic Routing Encapsulation (GRE)
This option is correct. GRE (Generic Routing Encapsulation) is a tunneling protocol used to encapsulate a wide variety of network layer protocols into IP tunnels. GRE is often used to create point-to-point connections across networks or to encapsulate non-IP traffic for transport across an IP network. It is widely supported across all Junos platforms, including routers and firewalls. GRE is versatile and allows the transmission of multicast traffic, making it suitable for creating VPNs, or for connecting remote sites.
Option C: IP-in-IP encapsulation (IP-IP)
This option is also correct. IP-in-IP encapsulation (IP-IP) is a simple tunneling mechanism where an entire IP packet is encapsulated inside another IP packet. This allows for the creation of a virtual point-to-point connection between devices, often used for simple tunneling scenarios or for VPN connections. IP-IP encapsulation is supported across all Junos platforms and is used to create tunnels for routing purposes, typically between network devices like routers. It is easy to configure and deploy for secure, private communication across the public internet or other untrusted networks.
Option D: IPsec tunnels for encrypted communication
While IPsec (Internet Protocol Security) is a powerful tunneling protocol used for creating secure encrypted tunnels, it is not supported across all Junos platforms in the same way that GRE and IP-IP are. IPsec is commonly used in VPN configurations to ensure the confidentiality and integrity of data being transmitted over potentially insecure networks. However, it requires hardware or software support for encryption and decryption processes, and in some cases, its use might be limited by platform capabilities or licensing requirements. Therefore, it’s not supported in all Junos platforms universally, unlike GRE and IP-IP.
The two tunneling protocols that are supported across all Junos platforms for traffic encapsulation are Generic Routing Encapsulation (GRE) and IP-in-IP encapsulation (IP-IP). These two options enable traffic encapsulation across various network topologies, supporting the transport of data through tunnels across different parts of the network.
Question 10:
Within a typical OSPF deployment on a Juniper router, what happens when two routers attempt to form a neighbor relationship but have mismatched hello/dead interval timers?
A. The routers form a full adjacency with reduced convergence time
B. The routers will continuously exchange LSAs without forming a neighbor relationship
C. The neighbor adjacency will fail, and the routers will not become neighbors
D. The router with the lower timer settings will adjust its intervals to match the other
Correct Answer: C
Explanation:
In an OSPF (Open Shortest Path First) deployment, routers must establish a neighbor relationship before exchanging Link-State Advertisements (LSAs) to synchronize their routing tables. One of the key parameters for forming a successful neighbor relationship is the hello and dead interval timers. These timers define how often routers send hello packets to each other and how long a router waits before declaring a neighbor down if no hello packets are received.
The hello interval determines how often OSPF hello packets are exchanged, while the dead interval defines how long a router will wait before considering a neighbor unreachable if no hello packets are received.
For OSPF routers to form an adjacency, the following conditions must be met:
The hello interval must be the same on both routers.
The dead interval must also be the same on both routers.
Other parameters, such as authentication and area type, must match.
If the hello interval and dead interval timers are mismatched between two routers, they will fail to establish a neighbor relationship. This mismatch prevents the routers from synchronizing their LSA exchanges and subsequently forming a full adjacency.
Option A: "The routers form a full adjacency with reduced convergence time"
This option is incorrect. A mismatch in hello and dead intervals prevents the formation of a full adjacency. The routers cannot establish a neighbor relationship until these timers are consistent across both routers.
Option B: "The routers will continuously exchange LSAs without forming a neighbor relationship"
This option is also incorrect. LSAs (Link-State Advertisements) are exchanged only once the routers have successfully formed a neighbor relationship. If the hello and dead intervals are mismatched, the routers will not be able to form a neighbor relationship, and therefore will not exchange LSAs.
Option C: "The neighbor adjacency will fail, and the routers will not become neighbors"
This option is correct. When the hello and dead interval timers do not match, the neighbor adjacency will fail, and the two routers will not become neighbors. This mismatch prevents OSPF from forming a stable connection between the routers and consequently impacts OSPF operations.
Option D: "The router with the lower timer settings will adjust its intervals to match the other"
This option is incorrect. OSPF does not automatically adjust the timer settings of one router to match the other. Both routers must have identical hello and dead intervals for a neighbour relationship to be successfully established. If one router has a different setting, the adjacency will fail unless the configuration is manually corrected.
When two routers have mismatched hello and dead intervals in an OSPF deployment, the neighbor adjacency will fail, and the routers will not become neighbors. This failure to form a neighbour relationship occurs because OSPF requires both routers to have matching timers to maintain synchronization.
