Juniper JN0-351 Enterprise Routing and Switching, Specialist Exam Practice Test

Answer : B, D

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.

Answer : A, B, C

Ais correct because you need to configure BGP multihop to enable redundancy for the EBGP peering between the two routers.BGP multihop is a feature that allows BGP peers to establish a session over multiple hops, instead of requiring them to be directly connected1.By default, EBGP peers use a time-to-live (TTL) value of 1 for their packets, which means that they can only reach adjacent neighbors1.However, if you configure BGP multihop with a higher TTL value, you can allow EBGP peers to communicate over multiple routers in between1. This can provide redundancy in case of a link failure or a router failure between the EBGP peers.

Bis correct because you need to configure loopback interface peering to enable redundancy for the EBGP peering between the two routers.Loopback interface peering is a technique that uses loopback interfaces as the source and destination addresses for BGP sessions, instead of physical interfaces2.Loopback interfaces are virtual interfaces that are always up and reachable as long as the router is operational2.By using loopback interface peering, you can avoid the dependency on a single physical interface or link for the BGP session, and use multiple paths to reach the loopback address of the peer2. This can provide redundancy and load balancing for the EBGP peering.

Cis correct because you need to configure routes for the peer loopback interface IP addresses to enable redundancy for the EBGP peering between the two routers.Routes for the peer loopback interface IP addresses are necessary to ensure that the routers can reach each other's loopback addresses over multiple hops2.You can use static routes or dynamic routing protocols to advertise and learn the routes for the peer loopback interface IP addresses2. Without these routes, the routers will not be able to establish or maintain the BGP session using their loopback interfaces.

Answer : B, D

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.

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.

Answer : D

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.

1:Configuring Keepalive Time and Hold time for a GRE Tunnel Interface2: keepalive | Junos OS | Juniper Networks3: Configuring Bidirectional Forwarding Detection4: event link-adjacency-loss | Junos OS | Juniper Networks5: Understanding Link Layer Discovery Protocol

Answer : C, D

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.

Answer : A

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.

1:rib-groups | Junos OS | Juniper Networks