JN0-351 Exam Dumps - Juniper JNCIS-ENT Questions and Answers

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 originated 1 .  This is done when the switch doesn’t know the destination MAC address or when the packet is a broadcast or multicast 1 .

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 received 2 3 .  This information is stored in a MAC address table, also known as a bridge table 2 3 .

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

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 state 2 .  It’s not a mechanism used in building and maintaining a Layer 2 bridge table 2 .

Junos devices support various types of tunnels for different purposes 1 2 .

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 network 1 .  Junos devices support GRE tunnels 1 .

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 session 1 .  Junos devices support IPsec tunnels 1 .

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 network 2 .

Option C is incorrect.  While Junos devices do support IP-IP (also known as IP tunneling), it’s not supported on all Junos devices 1 .

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 PICs 1 .

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 interfaces 2 . 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.

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.

The exhibit shows the configuration of BFD liveness detection for BGP at the global level, which applies to all BGP neighbors by default 1 .  However, this configuration does not specify the session mode, which determines whether BFD uses single-hop or multihop mode to communicate with a neighbor 2 .

For single-hop BGP neighbors, which are directly connected on the same subnet, the session mode can be either automatic or single-hop.  For multihop BGP neighbors, which are not directly connected and require multiple hops to reach, the session mode must be multihop 2 .

Since your BGP neighbors are in different countries, they are likely to be multihop neighbors.  Therefore, you need to configure the session mode as multihop for each neighbor individually at the [edit protocols bgp group group-name neighbor address bfd-liveness-detection] hierarchy level 2 . For example:

protocols { bgp { group usa { neighbor 192.0.2.1 { bfd-liveness-detection { session-mode multihop; } } } group france { neighbor 198.51.100.1 { bfd-liveness-detection { session-mode multihop; } } } } }

If you do not configure the session mode for multihop neighbors, BFD will use the default mode of automatic, which will try to use single-hop mode and fail to establish a BFD session with the remote neighbor 2 . This will prevent BGP from using BFD to detect liveliness and failover.

Therefore, the answer  B  is correct, as you need to configure the BFD liveness detection on the BGP neighbor level with the appropriate session mode for multihop neighbors.

The static route to the 0.0.0.0/0 network has a next hop of xe-0/0/0.0, which is a local interface. BGP does not accept static routes with a local interface as the next hop, because it cannot advertise them to other BGP peers. BGP requires a valid IP address as the next hop for static routes that are redistributed into BGP. To fix this issue, the static route should have a next hop of an IP address that is reachable via the xe-0/0/0.0 interface, such as the IP address of the eBGP neighbor. Alternatively, the next hop can be modified by using a route map when redistributing the static route into BGP12.

The other options are not correct because:

The as-path parameter is not required for redistributing static routes into BGP. The as-path attribute is automatically set by BGP when advertising routes to other BGP peers3.

A community string is not required for redistributing static routes into BGP. A community is an optional attribute that can be used to group routes and apply policies to them4.

The no-readvertise feature is not specified in the configuration. The no-readvertise feature is used to prevent routes learned from one iBGP peer from being advertised to another iBGP peer5.

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 devices 1 :

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 families 2 .

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 types 3 .

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 LAGs 4 .

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.

A  is correct because you can deploy only stateless firewall filters on an EX Series switch.  A stateless firewall filter is a filter that evaluates each packet individually based on the header information, such as source and destination addresses, protocol, and port numbers 1 .  A stateless firewall filter does not keep track of the state or context of a packet flow, such as the sequence number, flags, or session information 1 .  EX Series switches support only stateless firewall filters, which are also called access control lists (ACLs) or packet filters 2 .

C  is correct because you can apply firewall filters to both Layer 2 and Layer 3 traffic on an EX Series switch.  Layer 2 traffic is traffic that is switched within a VLAN or a bridge domain, while Layer 3 traffic is traffic that is routed between VLANs or networks 3 .  EX Series switches support three types of firewall filters: port (Layer 2) firewall filters, VLAN firewall filters, and router (Layer 3) firewall filters 4 . You can apply these filters to different interfaces and directions to control the traffic entering or exiting the switch.