Pass the Juniper JNCIS-ENT JN0-351 Questions and answers with CertsForce

According to the Juniper documentation 1 , MAC limiting is a feature that enhances port security by limiting the number of MAC addresses that can be learned within a VLAN. When the MAC limit is exceeded, the switch can perform different actions, such as ignoring, dropping, logging, shutting down, or disabling the offending port.  The default action is to drop the packets with new MAC addresses and log a message 2 . Therefore, the correct answer is B.

The other options are not correct because:

A. The switch will not shut down the offending port for five minutes by default.  This is a configurable action, but not the default one 2 .

C. The switch will not flood traffic out of all ports for the offending MAC address by default.  This is a possible consequence of ignoring the packets with new MAC addresses, but not the default action 2 .

D. The switch will not shut down MAC learning on the offending port for five minutes by default.  This is another configurable action, but not the default one 2 .

Both aggregate and generated routes would work, but the best choice is generated routes.

A route reflector is a BGP router that is allowed to break the iBGP loop avoidance rule and advertise routes received from an iBGP peer to another iBGP peer under specific conditions 1 .  A route reflector can have three types of peerings: EBGP neighbor, IBGP client neighbor, and IBGP non-client neighbor 2 .  A cluster is a group of route reflectors and their clients that are fully meshed 3 .  The cluster ID is a 4-byte value that identifies the route reflector cluster and is carried in the ORIGINATOR_ID attribute of the BGP update message 4 . The cluster ID is used to prevent routing loops among route reflectors and their clients.  If a route reflector receives a route with its own cluster ID, it discards the route 5 . Therefore, the cluster ID is required to prevent routing loops when using route reflectors.

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 endpoint 1 .

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 power 2 .

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.

On Juniper switches, the default VLAN is set to a VLAN ID of 1 by default 1 2 .  This means that all interfaces on the switch are members of VLAN 1 until they are specifically assigned to another VLAN 1 2 . Therefore, option A is correct.

The default VLAN ID can be changed 1 2 .  This allows network administrators to configure the switch to use a different VLAN as the default, if necessary 1 2 . Therefore, option D is correct.

According to the Juniper documentation 1 , the source and destination addresses of a GRE tunnel interface must be in different subnets. If they are in the same subnet, the router will not be able to route the GRE packets correctly. In the exhibit, the source and destination addresses are both in the 192.168.197.0/24 subnet, which is invalid for GRE tunneling. Therefore, the correct answer is D. References:  Configuring GRE Tunnel Interfaces | Junos OS

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 LAN 1 .  The DR election process is based on the following criteria, in order of precedence 1 :

The router with the highest OSPF priority becomes the DR. The default priority is 1, and a priority of 0 means the router will not participate in the election.

If there is a tie in priority, the router with the highest router ID becomes the DR. The router ID is a 32-bit number that uniquely identifies a router in an OSPF domain. It can be manually configured or automatically derived from the highest IP address of a loopback interface or a physical interface.

If there is a tie in router ID, the router that was first to become an OSPF neighbor becomes the DR.

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 fails 1 .