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

The exhibit shows the output of the command  show ip bgp , which displays information about the BGP routes in the routing table 1 . 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 route 2 .

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 precedence 3 .  The first attribute that is compared is weight, which is a Cisco-specific attribute that is local to the router 3 .  If the weight is equal or not set, the next attribute that is compared is local preference 3 .

In this case, both routes have the same weight of 0, which means that they are learned from external BGP (eBGP) peers 3 . 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 table 3 . The other attributes, such as origin code and AS path, are not considered in this case.

The feature that enables an interface on an EX Series switch to receive both untagged traffic (from the computer) and tagged traffic (from the IP phone) is the  voice VLAN 1 2 .

The voice VLAN feature in EX-series switches enables access ports to accept both data (untagged) and voice (tagged) traffic and separate that traffic into different VLANs 1 2 .  This allows the switch to differentiate between voice and data traffic, ensuring that voice traffic can be treated with a higher priority 1 2 . Therefore, option D is correct.

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.

A. The routes displayed have traversed one or more autonomous systems. True. The AS path attribute shows AS numbers (e.g., 65401 65520.), indicating the route ' s traversal through various autonomous systems. D. The routes displayed are being learned from an IBGP peer. True. The absence of the ' * > i ' marker before the prefixes indicates they are being learned from an IBGP peer. Therefore, the correct statements are A. The routes displayed have traversed one or more autonomous systems. and D. The routes displayed are being learned from an IBGP peer.

The Graceful Routing Engine Switchover (GRES) feature in Junos OS enables a router with redundant Routing Engines to continue forwarding packets, even if one Routing Engine fails 1 .  GRES preserves interface and kernel information, ensuring that traffic is not interrupted 1 .  However, GRES does not preserve the control plane 1 .

To preserve routing during a switchover, GRES must be combined with either Graceful Restart protocol extensions or Nonstop Active Routing (NSR) 1 .  When GRES is combined with NSR, nearly 75 percent of line rate worth of traffic per Packet Forwarding Engine remains uninterrupted during GRES 1 .  Any updates to the primary Routing Engine are replicated to the backup Routing Engine as soon as they occur 1 .

Therefore, when GRES is combined with NSR, routing is preserved and the new master RE does not restart rpd 1 .

 In a Rapid Spanning Tree Protocol (RSTP) topology, the root bridge is determined by the switch with the lowest bridge priority value 1 2 .  If all switches have the same priority, then the root bridge is assigned to the switch whose MAC address’s hex value is the lowest 2 .  The default bridge priority value is 32768 3 2 . However, without the actual exhibit, it’s difficult to definitively determine which device is the root bridge.  But based on the options provided, if we assume that the local device has a lower bridge priority or a lower MAC address than other devices in the network, then it could be considered as the root bridge for this RSTP topology 4 5 .

A keepalive OAM probe is a mechanism that can be used to monitor the state of a GRE tunnel and detect any failures in the tunnel path. A keepalive OAM probe consists of sending periodic packets from one end of the tunnel to the other and expecting a reply.  If no reply is received within a specified time, the tunnel is considered down and the line protocol of the tunnel interface is changed to down 1 .

To configure a keepalive OAM probe for a GRE tunnel, you need to specify two parameters: the keepalive-time and the hold-time. The keepalive-time is the interval between each keepalive packet sent by the local router.  The hold-time is the maximum time that the local router waits for a reply from the remote router before declaring the tunnel down 2 .

According to the Juniper Networks documentation, the hold-time value must be two times the keepalive-time value for a GRE tunnel 2 . This is because the hold-time value must account for both the round-trip time of the keepalive packet and the processing time of the remote router. If the hold-time value is too small, it may cause false positives and unnecessary tunnel flaps.

In the exhibit, the configuration shows that the keepalive-time is set to 10 seconds and the hold-time is set to 15 seconds for the gr-1/1/10.1 interface. This means that the local router will send a keepalive packet every 10 seconds and will wait for 15 seconds for a reply from the remote router. However, this hold-time value is not two times the keepalive-time value, which violates the recommended configuration. This may cause traffic drops if the remote router takes longer than 15 seconds to reply.

Therefore, option D is correct, because the hold-time value must be two times the keepalive-time value for a GRE tunnel.  Option A is incorrect, because BFD is not required for GRE tunnels; BFD is another protocol that can be used to monitor tunnels, but it is not compatible with GRE keepalives 3 .  Option B is incorrect, because the “event link-adjacency-loss” option is not related to GRE tunnels; it is an option that can be used to trigger an action when a link goes down 4 .  Option C is incorrect, because LLDP does not need to be removed from the gr-1/1/10.1 interface; LLDP is a protocol that can be used to discover neighboring devices and their capabilities, but it does not interfere with GRE tunnels 5 .

BGP is a routing protocol that operates between autonomous systems (AS). An AS is a group of routers under a single administrative control. BGP can be classified into two types: internal BGP (IBGP) and external BGP (EBGP). IBGP is the BGP communication between routers within the same AS, while EBGP is the BGP communication between routers in different AS. BGP uses the AS_PATH attribute to record the AS numbers that the route has passed through, and uses it to prevent routing loops and select the best path.

In this scenario, you want to add a second ISP connection and remove the default route to the existing ISP. This means that you want to have more control over the routing decisions and use BGP to exchange routes with both ISPs. To do this, you need to deploy the BGP protocol in your network and configure both IBGP and EBGP sessions. The correct statements about BGP in this scenario are:

IBGP peers advertise routes received from EBGP peers to other IBGP peers. This is the default behavior of IBGP, as it allows the routers within the same AS to learn the routes from different EBGP peers and select the best exit point. However, IBGP has a rule that it does not advertise routes received from IBGP peers to other IBGP peers, to avoid creating routing loops. Therefore, option B is correct and option C is incorrect. To overcome this rule, IBGP requires a full mesh topology, where every IBGP router is directly connected to every other IBGP router, or a route reflector or confederation design, where some IBGP routers act as intermediaries to reflect or aggregate the routes to other IBGP routers.

EBGP peers advertise routes received from IBGP peers to other EBGP peers. This is the default behavior of EBGP, as it allows the routers in different AS to exchange routes and reachability information. However, EBGP has a rule that it does not advertise routes received from EBGP peers to other EBGP peers, to avoid creating routing loops. Therefore, option D is correct and option A is incorrect. To overcome this rule, EBGP uses the AS_PATH attribute to filter out the routes that contain its own AS number, or uses route maps or policies to control the route advertisement. IBGP does not update the next-hop attribute to ensure reachability within an AS, as the next-hop attribute is preserved by IBGP. Instead, IBGP relies on an underlying IGP (Interior Gateway Protocol) to provide reachability to the next-hop.

A  is correct because generated routes require a contributing route.  A contributing route is a route that matches the destination prefix of the generated route and has a valid next hop 1 .  A generated route is only installed in the routing table if there is at least one contributing route available 2 . This ensures that the generated route is reachable and useful.  If there is no contributing route, the generated route is not added to the routing table 2 .

B  is correct because generated routes show a next hop in the routing table.  A generated route inherits the next hop of its primary contributing route, which is the most preferred route among all the contributing routes 2 .  The next hop of the generated route can be either an IP address or an interface name, depending on the type of the contributing route 2 .  The next hop of the generated route can also be modified by a routing policy 3 .