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

The output of the show bgp neighbor command shows the following information:

The local AS number of R1 is 65400, as indicated by the line “Local: 10.32.1.1+179 AS 65400”.

The peer AS number of 10.32.1.2 is 63645, as indicated by the line “Peer: 10.32.1.2+179 AS 63645”.

The BGP session is established, as indicated by the line “State: Established”.

The routers are exchanging IPv4 routes, as indicated by the line “Type: External State: Established Flags: < Sync > ” and the table showing the number of prefixes received and sent for inet.0 routing table. References:  Enterprise Routing and Switching, Specialist (JNCIS-ENT) - Juniper Networks , [show bgp neighbor - Technical Documentation - Support - Juniper Networks]

According to the Juniper documentation 1 , the output of the show vlans command displays the forwarding options for the VLAN, including the DHCP security features. In the exhibit, the output shows that DHCP security is enabled, and that ARP inspection and IP source guard are also enabled. These features work together to protect the switch from IP spoofing and ARP spoofing attacks. DHCP snooping builds a database of IP/MAC bindings by snooping DHCP messages. ARP inspection validates ARP packets against the DHCP snooping database and drops invalid packets.  IP source guard checks the IP and MAC source addresses of packets against the DHCP snooping database and drops spoofed packets 2 3 . Therefore, the correct answer is A, B, and C.

The other options are not correct because:

D. The DHCP snooping database is not protected by default.  To protect the database from corruption or loss, you need to configure a file name and a location for storing the database, and enable periodic write operations to the file 4 . The exhibit does not show any such configuration.

E. DHCP snooping is not enabled for IPv6 traffic by default.  To enable DHCPv6 snooping, you need to configure a DHCPv6 relay agent and specify the trusted interfaces for DHCPv6 messages 5 . The exhibit does not show any such configuration.

BGP has a simple loop prevention mechanism for eBGP that checks the AS path for its own AS number. However, this mechanism does not work for iBGP, since all routers in the same AS have the same AS number. Therefore, iBGP has two additional rules to prevent routing loops within an autonomous system:

A router does not advertise a route learned from an iBGP neighbor to another iBGP neighbor. This rule ensures that a route does not loop back to the original iBGP router through another iBGP path.

A router does not accept a route learned from an iBGP neighbor if the next hop is not reachable via an IGP. This rule ensures that a router does not forward packets to an unreachable next hop.

These two rules imply that iBGP sessions must be configured as a logical full mesh, meaning that every iBGP router must have a direct iBGP session with every other iBGP router in the same AS. This way, every iBGP router can learn the best route from the eBGP routers and use the IGP to reach the next hop. A logical full mesh does not require a physical full mesh, meaning that iBGP routers do not have to be directly connected. They can use intermediate routers to establish iBGP sessions, as long as the IGP can reach the next hop.

A logical full mesh can be challenging to scale and maintain, especially for large ASes with many iBGP routers. Therefore, some alternatives to the full mesh requirement have been developed, such as route reflectors and confederations. These alternatives relax the iBGP rules and introduce additional attributes and mechanisms to prevent routing loops, such as originator ID and cluster list. References:

BGP Fundamentals

BGP - eBGP loop prevention mechanism same AS number

Loop Prevention in BGP Routing

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.

Option A is correct. Creating multiple areas in OSPF can help to reduce the convergence time . This is because changes in one area do not affect other areas, so fewer routers need to run the SPF algorithm in response to a change.

Option D is correct. Creating multiple areas in OSPF can help to reduce Link State Advertisement (LSA) flooding across the network. This is because LSAs are not flooded out of their area of origin.

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 .

Option A is correct.  The storm control feature is enabled in the factory-default configuration on EX Series switches 1 2 .  On EX2200, EX3200, EX3300, EX4200, and EX6200 switches, the factory default configuration enables storm control for broadcast and unknown unicast traffic on all switch interfaces 2 .  On EX4300 switches, the factory default configuration enables storm control on all Layer 2 switch interfaces 1 .

Option B is incorrect.  The storm control feature does not require a special license on EX Series switches 3 4 .

Option C is incorrect. There’s no information available that suggests the storm control feature is not supported on aggregate Ethernet interfaces.

Option D is incorrect.  The storm control configuration applies to traffic at the ingress of an interface 5 , not just between the forwarding and control plane.

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 interface 1 .  Level 1 systems route within an area 2 .  If the destination is outside an area, Level 1 systems route toward a Level 2 system 2 . 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 Networks 1  and Cisco 3 4 .

To create a LAG interface, you need to perform two actions: enable LAG on the chassis and on each member interface. The first action is to configure the chassis stanza with the aggregated-devices statement and specify the number of LAG interfaces and the link-speed for each interface. The second action is to configure each member interface with the family ethernet-switching statement and the aggregated-ether-options statement with the lacp option. The name of the first LAG interface is not relevant, as long as it matches the name of the aggregated interface under the interfaces stanza. The name can be ae0, ae1, or any other valid name. References:

Enterprise Routing and Switching, Specialist (JNCIS-ENT) - Juniper Networks

Enterprise Routing and Switching, Specialist (JNCIS-ENT) - Juniper Networks

[Junos OS Layer 2 Configuration Guide - TechLibrary - Juniper Networks]

[Junos OS Layer 2 Configuration Guide - TechLibrary - Juniper Networks]