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

A  is correct because RSTP alternate ports block traffic while receiving superior BPDUs from a neighboring switch.  An alternate port is a backup port for a root port, which means it receives better BPDUs from another bridge than the current root port 1 .  However, an alternate port does not forward any traffic, as it is in a discarding state 2 . It only listens to BPDUs and waits for the root port to fail.  If the root port fails, the alternate port can immediately transition to a forwarding state and become the new root port 1 .

C  is correct because RSTP alternate ports provide an alternate higher cost path to the root bridge.  An alternate port is selected based on the same criteria as the root port, which are the lowest bridge ID, the lowest path cost, the lowest sender port ID, and the lowest receiver port ID 3 .  However, an alternate port receives a higher cost BPDU than the root port, otherwise it would be the root port itself 1 . Therefore, an alternate port provides an alternate higher cost path to the root bridge than the root port.

The bridging table is a data structure that stores the MAC addresses and the associated interface details and MAC learned time for each MAC address. The bridging table is used by the switch to forward frames based on the destination MAC address. The ether type details and the preamble of Ethernet packet are not stored in the bridging table, as they are not relevant for the switching process. 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]

The solution that should be implemented in this scenario is to create a default generate route that includes an import policy to match BGP routes from ISP1 and assign a preference value of four or less. This way, the default route will be advertised to the internal OSPF neighbors only when there is a BGP route from ISP1 in the routing table, and it will have a higher preference than any other default route from ISP2 or ISP3. If ISP1 is not available, the default generate route will be withdrawn and the traffic will use the next available default route from ISP2 or ISP3.

Option A is incorrect because creating a default static route with ISP1’s address as the next hop while specifying the addresses for ISP2 and ISP3 as qualified next hops with a preference value of six or higher will not ensure that the default route is advertised to the internal OSPF neighbors only when ISP1 is available. The default static route will always be in the routing table regardless of the availability of ISP1, and it will have a lower preference than any other default route from ISP2 or ISP3.

Option C is incorrect because creating a default static route with each neighbor address as the next hop will not ensure that all traffic uses ISP1 as the primary connection and only uses ISP2 and ISP3 when ISP1 is not available. The default static route will always be in the routing table regardless of the availability of ISP1, and it will load balance the traffic among the three ISPs.

Option D is incorrect because creating a default aggregated route will not ensure that the default route is advertised to the internal OSPF neighbors only when ISP1 is available. The default aggregated route will always be in the routing table regardless of the availability of ISP1, and it will not have any preference value associated with it. References:

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

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

In OSPF, the Designated Router (DR) and Backup Designated Router (BDR) are elected based on the priority of the routers 1 .  The router with the highest priority becomes the DR, and the router with the second highest priority becomes the BDR 1 .  If there is a tie in priority, then the router with the highest Router ID is chosen 1 .

In this scenario, R2 has a higher priority (64) than R1 (32), so R2 will become the DR 1 .  Since R1 has the second highest priority, it will become the BDR 1 . Therefore, option D is correct.

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 adjacencies 1 .  If the MTU is less than this, IS-IS adjacencies will not be established 1 .

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-IS 1 .  If the loopback interface is not included in IS-IS, it could prevent IS-IS adjacencies from being established 1 .

Therefore, options A and D are correct.

Redundant Trunk Groups (RTGs) on EX Series switches provide a simple solution for network recovery when a trunk port on a switch goes down 1 .  They are configured on the access switch and contain two links: a primary or active link, and a secondary link 1 .  Therefore, option B is correct because if the active link fails, the secondary link automatically starts forwarding data traffic without waiting for normal spanning-tree protocol convergence 1 .

Option D is also correct.  In a typical enterprise network composed of distribution and access layers, RTGs are used where one Access switch is connected to two different uplink switches 2 .  This implies that RTGs must be connected to the same aggregation switch 2 .

 References:  Configuring Layer 2 Firewall Filters - TechLibrary - Juniper Networks