Free Juniper JN0-351 Practice Exam with Questions & Answers | Set: 2

• According to the OSPF protocol, the designated router (DR) is the router that acts as the focal point for exchanging routing information on a multi-access network segment, such as a LAN1. The DR election process is based on the following criteria, in order of precedence1:
• In your scenario, two routers share the same highest priority and start time. This means that they have equal chances of becoming the DR based on the first and third criteria. Therefore, the second criterion will be used to break the tie, which is the router ID. The router with the highest router ID will become the DR, and the other router will become the backup designated router (BDR), which is ready to take over the role of DR if it fails1.

Aggregate routes are used for advertising summarized network prefixes12. 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 D is correct. Options A, B, and C are not correct because:

• Aggregate routes can be used with both static routing and dynamic routing protocols1.
• Aggregate routes are not automatically generated for all of the subnets in a routing table. They need to be manually configured1.
• Aggregate routes are not always preferred over more specific routes. The route selection process in Junos OS considers several factors, including route preference and metric, before determining the active route1.

• 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.

Option A suggests that the MTU is not at least 1492 bytes. This is correct because IS-IS requires a minimum MTU of 1492 bytes to establish adjacencies1. If the MTU is less than this, IS-IS adjacencies will not be established1.

Option D suggests that the lo0 interface is not included as an IS-IS interface. This is also correct because the loopback interface (lo0) is typically used as the router ID in IS-IS1. If the loopback interface is not included in IS-IS, it could prevent IS-IS adjacencies from being established1.

Therefore, options A and D are correct.

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.

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.

Option A is correct. For traffic to be sent through a GRE tunnel, there must be a route that directs the traffic into the tunnel. This is typically accomplished through the use of a static route or a dynamic routing protocol.

Option B is correct. All intermediary devices must have a route to the tunnel endpoints34. In real-world scenarios, the tunnel endpoints for a tunnel going over the Internet must have globally reachable internet addresses. Otherwise, intermediate routers in the Internet cannot forward the tunneled packets.

In OSPF, the state of the neighbor relationship is determined by the exchange of OSPF packets between routers1. The state “2Way” as shown in the exhibit indicates that bi-directional communication has been established between the two OSPF routers1. This is the normal state for a neighbor that is not the Designated Router (DR) or Backup Designated Router (BDR) on a broadcast, non-broadcast multi-access (NBMA), or point-to-multipoint network1. These neighbors are often referred to as "DRothers"1. Therefore, option B is correct.

A tunnel is a connection between two computer networks, in which data is sent from one network to another through an encrypted link. Tunnels are commonly used to secure data communications between two networks or to connect two networks that use different protocols.

Option B is correct, because tunnel endpoints must have a valid route to the remote tunnel endpoint. A tunnel endpoint is the device that initiates or terminates a tunnel connection. For a tunnel to be established, both endpoints must be able to reach each other over the underlying network. This means that they must have a valid route to the IP address of the remote endpoint1.

Option D is correct, because tunnels add additional overhead to packet size. Tunnels work by encapsulating packets: wrapping packets inside of other packets. This means that the original packet becomes the payload of the surrounding packet, and the surrounding packet has its own header and trailer. The header and trailer of the surrounding packet add extra bytes to the packet size, which is called overhead. Overhead can reduce the efficiency and performance of a network, as it consumes more bandwidth and processing power2.

Option A is incorrect, because BFD can be used to monitor tunnels. 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. BFD can also be used to monitor the connectivity of tunnels, such as GRE, IPsec, or MPLS.

Option C is incorrect, because IP-IP tunnels are stateless. IP-IP tunnels are a type of tunnels that use IP as both the encapsulating and encapsulated protocol. IP-IP tunnels are simple and easy to configure, but they do not provide any security or authentication features. IP-IP tunnels are stateless, which means that they do not keep track of the state or status of the tunnel connection. Stateless tunnels do not require any signaling or negotiation between the endpoints, but they also do not provide any error detection or recovery mechanisms.

References:

1: What is Tunneling? | Tunneling in Networking 2: What Is Tunnel In Networking, Its Types, And Its Benefits? : [Configuring Bidirectional Forwarding Detection] : [IP-IP Tunneling]