JN0-351 Enterprise Routing and Switching Specialist (JNCIS-ENT) Questions and Answers

The feature that enables an interface on an EX Series switch to receive both untagged traffic (from the computer) and tagged traffic (from the IP phone) is the voice VLAN12.

The voice VLAN feature in EX-series switches enables access ports to accept both data (untagged) and voice (tagged) traffic and separate that traffic into different VLANs12. This allows the switch to differentiate between voice and data traffic, ensuring that voice traffic can be treated with a higher priority12. Therefore, option D is correct.

Junos devices support various types of tunnels for different purposes12.

• Option B is correct. Generic Routing Encapsulation (GRE) is a tunneling protocol that can encapsulate a wide variety of network layer protocols inside virtual point-to-point links over an Internet Protocol network1. Junos devices support GRE tunnels1.
• Option D is correct. IPsec (Internet Protocol Security) is a protocol suite for securing Internet Protocol (IP) communications by authenticating and encrypting each IP packet of a communication session1. Junos devices support IPsec tunnels1.
• Option A is incorrect. Spanning Tree Protocol (STP) is not a type of tunnel. It’s a network protocol designed to prevent loops in a bridged Ethernet local area network2.
• Option C is incorrect. While Junos devices do support IP-IP (also known as IP tunneling), it’s not supported on all Junos devices1.

The management IP address of a device is the IP address that is used to access the device for configuration and monitoring purposes. It is usually assigned to a dedicatedmanagement interface that is separate from the data interfaces. The management interface can be accessed via SSH, Telnet, HTTP, or other protocols.

In the exhibit, the list of interfaces and their statuses shows that the management interface isme0. This interface has an admin status ofup, a protocol status ofinet, a local address of172.23.12.100/24, and a remote address ofunspecified. This means that the me0 interface is active, has an IPv4 address assigned, and is not connected to another device.

Therefore, the management IP address of the device shown in the exhibit is172.23.12.100.

References:

[Management Interfaces Overview] : [Displaying Interface Status Information]

The correct answer to your question is C. Option C. Here is why:

• Option C shows the configuration of the chassis statement, which defines the properties of the router chassis, such as the number of aggregated Ethernet interfaces, the number of FPCs, and the number of PICs1.
• To enable aggregated Ethernet interfaces on a router, you need to specify the aggregated-devices statement under the chassis statement and set the ethernet parameter to the desired number of interfaces2. For example, to enable two aggregated Ethernet interfaces, you can use the following configuration:

chassis { aggregated-devices { ethernet { device-count 2; } } }

• Option C shows this configuration with the device-count set to 2, which will enable two aggregated Ethernet interfaces on the router. The other options do not show this configuration and will not enable any aggregated Ethernet interfaces on the router.
• Therefore, option C is the correct answer to your question.

• 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.

A keepalive OAM probe is a mechanism that can be used to monitor the state of a GRE tunnel and detect any failures in the tunnel path. A keepalive OAM probe consists of sending periodic packets from one end of the tunnel to the other and expecting a reply. If no reply is received within a specified time, the tunnel is considered down and the line protocol of the tunnel interface is changed to down1.

To configure a keepalive OAM probe for a GRE tunnel, you need to specify two parameters: the keepalive-time and the hold-time. The keepalive-time is the interval between each keepalive packet sent by the local router. The hold-time is the maximum time that the local router waits for a reply from the remote router before declaring the tunnel down2.

According to the Juniper Networks documentation, the hold-time value must be two times the keepalive-time value for a GRE tunnel2. This is because the hold-time value must account for both the round-trip time of the keepalive packet and the processing time of the remote router. If the hold-time value is too small, it may cause false positives and unnecessary tunnel flaps.

In the exhibit, the configuration shows that the keepalive-time is set to 10 seconds and the hold-time is set to 15 seconds for the gr-1/1/10.1 interface. This means that the local router will send a keepalive packet every 10 seconds and will wait for 15 seconds for a reply from the remote router. However, this hold-time value is not two times the keepalive-time value, which violates the recommended configuration. This may cause traffic drops if the remote router takes longer than 15 seconds to reply.

Therefore, option D is correct, because the hold-time value must be two times the keepalive-time value for a GRE tunnel. Option A is incorrect, because BFD is not required for GRE tunnels; BFD is another protocol that can be used to monitor tunnels, but it is not compatible with GRE keepalives3. Option B is incorrect, because the “event link-adjacency-loss” option is not related to GRE tunnels; it is an option that can be used to trigger an action when a link goes down4. Option C is incorrect, because LLDP does not need to be removed from the gr-1/1/10.1 interface; LLDP is a protocol that can be used to discover neighboring devices and their capabilities, but it does not interfere with GRE tunnels5.

References:

1: Configuring Keepalive Time and Hold time for a GRE Tunnel Interface 2: keepalive | Junos OS | Juniper Networks 3: Configuring Bidirectional Forwarding Detection 4: event link-adjacency-loss | Junos OS | Juniper Networks 5: Understanding Link Layer Discovery Protocol

The BGP attribute that you would use to forward all Internet traffic through the R1 device is the local preference1.

The local preference is an attribute that is used within an autonomous system (AS) and exchanged between iBGP routers1. It is used to select an exit point from the AS1. The path with the highest local preference is preferred1. By setting a higher local preference for the routes received from R1, you can make R1 the preferred exit point for all Internet traffic1.

• A is correct because dynamic ARP inspection (DAI) is a Layer 2 security feature that prevents ARP spoofing attacks. ARP spoofing is a technique that allows an attacker to send fake ARP messages to associate a spoofed MAC address with a legitimate IP address. This can result in traffic redirection, man-in-the-middle attacks, or denial-of-service attacks. DAI validates ARP packets by checking the source MAC address and IP address against a trusted database, which is usually built by DHCP snooping1. DAI discards any ARP packets that do not match the database or have invalid formats1.
• C is correct because DHCP snooping is a Layer 2 security feature that prevents DHCP spoofing attacks. DHCP spoofing is a technique that allows an attacker to act as a rogue DHCP server and offer fake IP addresses and other network parameters to unsuspecting clients. This can result in traffic redirection, man-in-the-middle attacks, or denial-of-service attacks. DHCP snooping filters DHCP messages by classifying switch ports as trusted or untrusted. Trusted ports are allowed to send and receive any DHCP messages, while untrusted ports are allowed to send only DHCP requests and receive only valid DHCP replies from trusted ports2. DHCP snooping also builds a database of MAC addresses, IP addresses, lease times, and binding types for each client2.

OSPF DR/BDR election is a process that occurs on multi-access data links. It is intended to select two OSPF nodes: one to be acting as the Designated Router (DR), and another to be acting as the Backup Designated Router (BDR).The DR and BDR are responsible for generating network LSAs for the multi-access network and synchronizing the LSDB with other routers on the same network1.

The DR/BDR election is based on two criteria: the OSPF priority and the router ID. The OSPF priority is a value between 0 and 255 that can be configured on each interface participating in OSPF. The default priority is 1. A priority of 0 means that the router will not participate in the election and will never become a DR or BDR. The router with the highest priority will become the DR, and the router with the second highest priority will become the BDR. If there is a tie in priority, then the router ID is used as a tie-breaker. The router ID is a 32-bit number that uniquely identifies each router in an OSPF domain.It can be manually configured or automatically derived from the highest IP address on a loopback interface or any active interface2.

In this scenario, all routers have the same priority of 1, so the router ID will determine the outcome of the election. The router IDs are shown in the exhibit as RID values. The highest RID belongs to R4 (10.10.10.4), so R4 will become the DR. The second highest RID belongs to R3 (10.10.10.3), so R3 will become the BDR.

References:

1:OSPF DR/BDR Election: Process, Configuration, and Tuning2:OSPF Designated Router (DR) and Backup Designated Router (BDR)

• A is correct because the interface is configured as a disabled port. A disabled port does not forward any traffic, including DHCP packets. Therefore, DHCP snooping cannot learn any MAC addresses or lease information from a disabled port1.
• C is correct because the interface is configured as a trunk port. By default, all trunk ports on the switch are trusted for DHCP snooping2. This means that DHCP snooping does not inspect or filter any DHCP packets received on a trunk port. Therefore, DHCP snooping does not add any entries to the snooping database for a trunk port2.

BGP attributes are properties that BGP uses for route advertisement, path selection, and loop prevention1. There are four categories of BGP attributes123:

• Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers123.
• Well-known discretionary: Supported by all BGP implementations, and are optionally included in BGP updates1.
• Optional transitive: May not be supported by all implementations of BGP1.
• Optional non-transitive: May not be supported by all implementations of BGP1.

The well-known mandatory attributes must be supported by all BGP implementations and must be included in every update123. These include the AS path and next hop attributes23. Therefore, options A and C are correct.

In this scenario, you should create an aggregate route1. Aggregate routes are used for advertising summarized network prefixes1. They help minimize the number of routing tables in an IP network by consolidating selected multiple routes into a single route advertisement1. This approach is in contrast to non-aggregation routing, in which every routing table contains a unique entry for each route1.

Therefore, option A is correct. Options B, C, and D are not correct because:

• Static route using the resolve feature: This type of route uses the resolve feature to install a static route in the routing table only if a specific condition is met1. However, it does not provide the capability to summarize multiple routes into a single prefix.
• Generate route: This type of route generates a route that is always present in the routing table and can be used to summarize routes. However, it does not have the capability to only advertise the route when specific BGP routes are being received from a neighbor1.
• Static route using qualified next hops: This type of route allows for the specification of multiple next-hop addresses for a static route1. However, it does not provide the capability to summarize multiple routes into a single prefix.

• 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.

The routers that are directly connected to the Dallas and Denver subnets are not advertising the connected subnets. This can be resolved by redistributing the connected subnets into OSPF1.

Option C suggests to configure and apply a routing policy that redistributes the connected Dallas and Denver subnets. This is correct because redistribution allows routes from one routing protocol to be communicated to another, and in this case, it allows the connected subnets to be advertised through OSPF1.

Option D suggests enabling the passive option on the OSPF interfaces that are connected to the Dallas and Denver subnets. This is also correct because in OSPF, a passive interface is an interface that belongs to the OSPF router, but does not send OSPF Hello packets1. It’s typically used on an interface that you don’t want to use for OSPF adjacencies, but you still want to advertise its IP address1. Therefore, enabling passive interface can help in advertising the Dallas and Denver subnets.

BGP (Border Gateway Protocol) is a protocol designed to exchange routing and reachability information among autonomous systems (AS) on the internet1.

• Option A is correct. When an EBGP router advertises routes to its neighbors, it appends its AS number to the AS_PATH attribute1. This is a key mechanism in BGP to prevent routing loops1.
• Option C is correct. BGP has a built-in loop prevention mechanism whereby if a BGP router detects its own AS in the AS_PATH attribute, it will drop the prefix and will not continue to advertise it2. This helps to prevent routing loops2.
• Option B is incorrect. EBGP routers do not accept routes that contain their own AS number in the AS_PATH2. Instead, they drop such routes as part of the loop prevention mechanism2.
• Option D is incorrect. While it’s true that EBGP routers append their AS number when advertising routes, they do not prepend their AS number1. The term “prepend” in BGP usually refers to a technique used to influence path selection by artificially lengthening the AS_PATH3.

The configuration shown in the exhibit is an example of a routing instance of type virtual-router. A routing instance is a collection of routing tables, interfaces, and routing protocol parameters that create a separate routing domain on a Juniper device1. A virtual-router routing instance allows administrators to divide a device into multiple independent virtual routers, each with its own routing table2.

The configuration also includes a rib-group statement, which is used to import routes from one routing table to another. A rib-group consists of an import-rib statement, which specifies the source routing table, and an export-rib statement, which specifies the destination routing table.

In this case, the rib-group name is inet-to-ispi, and the import-rib statement specifies inet.0 as the source routing table. The export-rib statement specifies ispi.inet.0 as the destination routing table. This means that the routes from inet.0 will be imported into ispi.inet.0.

Therefore, the correct answer is B. The inet.0 route table will be imported into the ispi.inet.0 route table.

References:

1: Routing Instances Overview 2: Virtual Routing Instances : [rib-group (Routing Options)]