Juniper Enterprise Routing and Switching Specialist (JNCIS-ENT) JN0-351 Exam Dumps: Updated Questions & Answers (October 2025)

BFD is a protocol that can be used to quickly detect failures in the forwarding path between two adjacent routers or switches. BFD can be integrated with various routing protocols and link aggregation protocols to provide faster convergence and fault recovery.

According to the Juniper Networks documentation, the following protocols support BFD on Junos OS devices1:

BGP: BFD can be used to monitor the connectivity between BGP peers and trigger a session reset if a failure is detected. BFD can be configured for both internal and external BGP sessions, as well as for IPv4 and IPv6 address families2.

OSPF: BFD can be used to monitor the connectivity between OSPF neighbors and trigger a state change if a failure is detected. BFD can be configured for both OSPFv2 and OSPFv3 protocols, as well as for point-to-point and broadcast network types3.

LACP: BFD can be used to monitor the connectivity between LACP members and trigger a link state change if a failure is detected. BFD can be configured for both active and passive LACP modes, as well as for static and dynamic LAGs4.

Other protocols that support BFD on Junos OS devices are:

IS-IS: BFD can be used to monitor the connectivity between IS-IS neighbors and trigger a state change if a failure is detected. BFD can be configured for both level 1 and level 2 IS-IS adjacencies, as well as for point-to-point and broadcast network types.

RIP: BFD can be used to monitor the connectivity between RIP neighbors and trigger a route update if a failure is detected. BFD can be configured for both RIP version 1 and version 2 protocols, as well as for IPv4 and IPv6 address families.

VRRP: BFD can be used to monitor the connectivity between VRRP routers and trigger a priority change if a failure is detected. BFD can be configured for both VRRP version 2 and version 3 protocols, as well as for IPv4 and IPv6 address families.

The protocols that do not support BFD on Junos OS devices are:

RSTP: RSTP is a spanning tree protocol that provides loop prevention and rapid convergence in layer 2 networks. RSTP does not use BFD to detect link failures, but relies on its own hello mechanism that sends BPDU packets every 2 seconds by default.

FTP: FTP is an application layer protocol that is used to transfer files between hosts over a TCP connection. FTP does not use BFD to detect connection failures, but relies on TCP’s own retransmission and timeout mechanisms.

References:

1: [Configuring Bidirectional Forwarding Detection] 2: [Configuring Bidirectional Forwarding Detection for BGP] 3: [Configuring Bidirectional Forwarding Detection for OSPF] 4: [Configuring Bidirectional Forwarding Detection for Link Aggregation Control Protocol] : [Configuring Bidirectional Forwarding Detection for IS-IS] : [Configuring Bidirectional Forwarding Detection for RIP] : [Configuring Bidirectional Forwarding Detection for VRRP] : [Understanding Rapid Spanning Tree Protocol] : [Understanding FTP]

The two reasons for the failure to form an adjacency in a network running IS-IS could be:

B. There is no configured ISO address on any IS-IS interface. IS-IS requires each router interface to have an ISO address configured. Without this address, the routers cannot form an adjacency1.

D. The family iso configuration is missing from the adjacency interface. The ‘family iso’ configuration is essential for IS-IS to function correctly. If this configuration is missing from the adjacency interface, it could prevent the formation of an adjacency1.

These explanations are based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks23.

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.

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)

In BGP, the path selection process is based on a set of attributes1. The process starts by preferring the path with the highest weight, then the highest local preference, then the locally originated routes, and so on1. If all these attributes are the same, then it prefers the path with the shortest AS path1.

Referring to the exhibit, all four ISPs have the same weight, local preference, and origin1. However, ISP 4 has the shortest AS path1. Therefore, ISP 4 will be selected as the active path. So, option C is correct.

 In a Rapid Spanning Tree Protocol (RSTP) topology, the root bridge is determined by the switch with the lowest bridge priority value12. If all switches have the same priority, then the root bridge is assigned to the switch whose MAC address’s hex value is the lowest2. The default bridge priority value is 3276832. However, without the actual exhibit, it’s difficult to definitively determine which device is the root bridge. But based on the options provided, if we assume that the local device has a lower bridge priority or a lower MAC address than other devices in the network, then it could be considered as the root bridge for this RSTP topology45.

On Juniper switches, the default VLAN is set to a VLAN ID of 1 by default12. This means that all interfaces on the switch are members of VLAN 1 until they are specifically assigned to another VLAN12. Therefore, option A is correct.

The default VLAN ID can be changed12. This allows network administrators to configure the switch to use a different VLAN as the default, if necessary12. Therefore, option D is correct.

A RIB group is a configuration that allows a routing protocol to install routes into multiple routing tables in Junos OS. 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 or group. A RIB group can also include an import-policy statement, which specifies one or more policies to control which routes are imported into the destination routing table or group1.

An import policy is a policy statement that defines the criteria for accepting or rejecting routes from the source routing table. An import policy can also modify the attributes of the imported routes, such as preference, metric, or community. An import policy can be applied to a RIB group by using the import-policy statement under the [edit routing-options rib-groups] hierarchy level1.

Therefore, option A is correct, because an import policy is applied to the RIB group to control which routes are installed in the destination routing table or group. Option B is incorrect, because all routes in the source routing table are imported into the destination routing table or group, unless filtered by an import policy. Option C is incorrect, because a firewall filter is not used to install routes in the RIB groups; a firewall filter is used to filter packets based on various criteria. Option D is incorrect, because an export policy is not applied to the RIB group; an export policy is applied to a routing protocol to control which routes are advertised to other devices.

References:

1: rib-groups | Junos OS | Juniper Networks

The default MAC age-out timer on an EX Series switch is 300 seconds12. The MAC age-out timer is the maximum time that an entry can remain in the MAC table before it “ages out,” or is removed31. This configuration can influence efficiency of network resource use by affecting the amount of traffic that is flooded to all interfaces1. When traffic is received for MAC addresses no longer in the Ethernet routing table, the router floods the traffic to all interfaces1.