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A is correct because when an OSPF adjacency is established, a router will advertise a connected network to OSPF neighbors. An OSPF adjacency is a logical relationship between two routers that agree to exchange routing information using the OSPF protocol1. To establish an OSPF adjacency, the routers must be in the same area, have compatible parameters, and exchange hello packets1. Once an OSPF adjacency is formed, the routers will exchange database description (DBD) packets, which contain summaries of their link-state databases (LSDBs)1. The LSDBs include information about the connected networks and their costs2. Therefore, when an OSPF adjacency is established, a router will advertise a connected network to OSPF neighbors through DBD packets.

D is correct because when a static route to the 224.0.0.5 address is created, a router will advertise a connected network to OSPF neighbors. The 224.0.0.5 address is the multicast address for all OSPF routers3. A static route to this address can be used to send OSPF hello packets to all OSPF neighbors on a network segment3. This can be useful when the network segment does not support multicast or when the router does not have an IP address on the segment3. When a static route to the 224.0.0.5 address is created, the router will send hello packets to this address and establish OSPF adjacencies with other routers on the segment3. As explained above, once an OSPF adjacency is formed, the router will advertise a connected network to OSPF neighbors through DBD packets.

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.

When the MAC address limit feature with the shutdown action is implemented on a switch, if a violation occurs, the interface is disabled and a system log entry is generated1. If the switch has been configured with the port-error-disable statement, the disabled interface recovers automatically upon expiration of the specified disable timeout1. However, if the switch has not been configured for auto-recovery from port error disabled conditions, you must manually clearthe violation by running the clear ethernet-switching port-error command for the interface to send and receive traffic again1. This explanation is based on the Enterprise Routing and Switching Specialist (JNCIS-ENT) documents and learning resources available at Juniper Networks1.

Option B is correct. Flooding is a mechanism used in Layer 2 bridging where the switch sends incoming packets to all its ports except for the port where the packet originated1. This is done when the switch doesn’t know the destination MAC address or when the packet is a broadcast or multicast1.

Option C is correct. Learning is another mechanism used in Layer 2 bridging where the switch learns the source MAC addresses of incoming packets and associates them with the port on which they were received23. This information is stored in a MAC address table, also known as a bridge table23.

Option A is incorrect. Blocking is a state in Spanning Tree Protocol (STP) used to prevent loops in a network2. It’s not a mechanism used in building and maintaining a Layer 2 bridge table2.

Option D is incorrect. Listening is also a state in Spanning Tree Protocol (STP) where the switch listens for BPDUs to make sure no loops occur in the network before transitioning to the learning state2. It’s not a mechanism used in building and maintaining a Layer 2 bridge table2.

A. On R1, enable Level 1 on the ge-0/0/1 interface. In IS-IS, both levels (Level 1 and Level 2) are enabled by default when you enable IS-IS on an interface1. Level 1 systems route within an area2. If the destination is outside an area, Level 1 systems route toward a Level 2 system2. Therefore, enabling Level 1 on the ge-0/0/1 interface on R1 would allow packets to reach from R1 to R3.

D. On R3 enable Level 1 on the ge-0/0/4 interface Similarly, enabling Level 1 on the ge-0/0/4 interface on R3 would allow packets to reach from R1 to R3.

These explanations are based on the IS-IS configuration documents and learning resources available at Juniper Networks1 and Cisco34.

The exhibit shows the output of the command show ip bgp, which displays information about the BGP routes in the routing table1. The output shows two routes for the destination 192.168.10.0/24, one from R1 and one from R2.

The route from R1 has a local preference of 200, while the route from R2 has a local preference of 100. Local preference is a BGP attribute that indicates the degree of preference for a route within an autonomous system (AS)2. A higher local preference means a more preferred route2.

BGP uses a best path selection algorithm to choose the best route for each destination among multiple paths. The algorithm compares different attributes of the routes in a specific order of precedence3. The first attribute that is compared is weight, which is a Cisco-specific attribute that is local to the router3. If the weight is equal or not set, the next attribute that is compared is local preference3.

In this case, both routes have the same weight of 0, which means that they are learned from external BGP (eBGP) peers3. Therefore, the next attribute that is compared is local preference. Since R1’s route has a higher local preference than R2’s route, it is chosen as the best path and installed in the routing table3. The other attributes, such as origin code and AS path, are not considered in this case.

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]

In OSPF, the Designated Router (DR) and Backup Designated Router (BDR) are elected based on the priority of the routers1. The router with the highest priority becomes the DR, and the router with the second highest priority becomes the BDR1. If there is a tie in priority, then the router with the highest Router ID is chosen1.

In this scenario, R2 has a higher priority (64) than R1 (32), so R2 will become the DR1. Since R1 has the second highest priority, it will become the BDR1. Therefore, option D is correct.

The exhibit shows the configuration of RSTP on EX-4, which has the command force-version stp. This command forces the switch to use the legacy STP protocol instead of RSTP, even though the switch supports RSTP1. This means that EX-4 will not be able to take advantage of the faster convergence and enhanced features of RSTP, such as edge ports, link type, and proposal/agreement sequence2.

The other switches in the network are likely to be running RSTP, as it is the default protocol for EX Series switches3. Therefore, there will be a compatibility issue between EX-4 and the other switches, which will result in longer convergence times and suboptimal performance. The switch will also generate a warning message that says “Warning: STP version mismatch with neighbor” when it receives a BPDU from a RSTP neighbor1.

To solve this problem, the force-version command must be removed from EX-4, so that it can run RSTP natively and interoperate with the other switches in the network. This will enable faster convergence and better stability for the network topology. To remove the command, you can use the delete protocols rstp force-version command in configuration mode1.

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.