Free Juniper JN0-351 Exam Actual Questions

The questions for JN0-351 were last updated On Nov 18, 2024

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Question No. 1

In RSTP, which three port roles are associated with the discarding state? (Choose three.)

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Correct Answer: B, C, D

In Rapid Spanning Tree Protocol (RSTP), there are several port roles that determine the behavior of the port in the spanning tree123.The roles include root, designated, alternate, backup, and disabled123.

The discarding state is associated with the backup, alternate, and disabled roles123.In a stable topology with consistent port roles throughout the network, RSTP ensures that every root port and designated port immediately transition to the forwarding state while all alternate and backup ports are always in the discarding state2.Disabled ports are also in the discarding state3.

Therefore, options B, C, and D are correct.


Question No. 2

What is a purpose of using a spanning tree protocol?

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Correct Answer: B

A broadcast storm is a network condition where a large number of broadcast packets are sent and received by multiple devices, causing congestion and performance degradation1.A broadcast storm can occur when there are loops in the network topology, meaning that there are multiple paths between two devices2.

A spanning tree protocol is a network protocol that prevents loops from being formed when switches or bridges are interconnected via multiple paths.It does this by creating a logical tree structure that spans all the devices in the network, and disabling or blocking the links that are not part of the tree, leaving a single active path between any two devices3.

By eliminating loops, a spanning tree protocol also eliminates broadcast storms, as broadcast packets will not be forwarded endlessly along the looped paths.Instead, broadcast packets will be sent only along the tree structure, reaching each device once and avoiding congestion3.


Question No. 3

What is the maximum allowable MTU size for a default GRE tunnel without IPv4 traffic fragmentation?

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Correct Answer: D

The maximum allowable MTU size for a default GRE tunnel without IPv4 traffic fragmentation is1476 bytes1.This is because GRE packets are formed by the addition of the original packets and the required GRE headers1.These headers are 24-bytes in length and since these headers are added to the original frame, depending on the original size of the packet we may run into IP MTU problems1.The most common IP MTU is 1500-bytes in length (Ethernet)1.When the tunnel is created, it deducts the 24-bytes it needs to encapsulate the passenger protocols and that is the IP MTU it will use1.For example, if we are forming a tunnel over FastEthernet (IP MTU 1500) the IOS calculates the IP MTU on the tunnel as: 1500-bytes from Ethernet - 24-bytes for the GRE encapsulation = 1476-Bytes1.


Question No. 4

Which statement is correct about the IS-IS ISO NET address?

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Correct Answer: B

An ISO NET address is a type of network address used by the IS-IS routing protocol.It identifies a point of connection to the network, such as a router interface, and is also called a Network Service Access Point (NSAP)1.

An ISO NET address consists of three parts: an area ID, a system ID, and a selector2. The area ID identifies the IS-IS area to which the device belongs. The system ID uniquely identifies the device within the area.The selector identifies a specific service or function on the device, such as routing or management2.

An ISO NET address must be unique for each device in the network, because it is used by IS-IS to establish adjacencies, exchange routing information, and compute shortest paths2. If two devices have the same ISO NET address, they will not be able to communicate with each other or with other devices in the network. Therefore, it is important to assign different ISO NET addresses to each device in the network.


Question No. 5

You are asked to create a new firewall filter to evaluate Layer 3 traffic that is being sent between VLANs. In this scenario, which two statements are correct? (Choose two.)

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Correct Answer: C, D

A firewall filter is a configuration that defines the rules that determine whether to forward or discard packets at specific processing points in the packet flow. A firewall filter can also modify the attributes of the packets, such as priority, marking, or logging.A firewall filter can be applied to various interfaces, protocols, or routing instances on a Juniper device1.

A firewall filter has a family attribute, which specifies the type of traffic that the filter can evaluate.The family attribute can be one of the following: inet, inet6, mpls, vpls, iso, or ethernet-switching2. The family inet firewall filter is used to evaluate IPv4 traffic, which is the most common type of Layer 3 traffic on a network.

To create a family inet firewall filter, you need to specify the appropriate match criteria and actions for each term in the filter. The match criteria can include various fields in the IPv4 header, such as source address, destination address, protocol, port number, or DSCP value.The actions can include accept, discard, reject, count, log, policer, or next term3.

To apply a firewall filter to Layer 3 traffic that is being sent between VLANs, you need to apply the filter to the appropriate IRB interface. An IRB interface is an integrated routing and bridging interface that provides Layer 3 functionality for a VLAN on a Juniper device. An IRB interface has an IP address that acts as the default gateway for the hosts in the VLAN.An IRB interface can also participate in routing protocols and forward packets to other VLANs or networks4.

Therefore, option C is correct, because you should create a family inet firewall filter with the appropriate match criteria and actions. Option D is correct, because you should apply the firewall filter to the appropriate IRB interface.

Option A is incorrect, because you should not create a family ethernet-switching firewall filter with the appropriate match criteria and actions. A family ethernet-switching firewall filter is used to evaluate Layer 2 traffic on a Juniper device.A family ethernet-switching firewall filter can only match on MAC addresses or VLAN IDs, not on IP addresses or protocols5.

Option B is incorrect, because you should not apply the firewall filter to the appropriate VLAN. A VLAN is a logical grouping of hosts that share the same broadcast domain on a Layer 2 network. A VLAN does not have an IP address or routing capability.A firewall filter cannot be applied directly to a VLAN; it must be applied to an interface that belongs to or connects to the VLAN6.


1:Firewall Filters Overview2:Configuring Firewall Filters3:Configuring Firewall Filter Match Conditions and Actions4:Understanding Integrated Routing and Bridging Interfaces5: Configuring Ethernet-Switching Firewall Filters6: Understanding VLANs

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