Free Practice Questions for Juniper JN0-351 Exam

A broadcast storm is a network condition where a large number of broadcast packets are sent and received by multiple devices, causing congestion and performance degradation 1 .  A broadcast storm can occur when there are loops in the network topology, meaning that there are multiple paths between two devices 2 .

A spanning tree protocol is a network protocol that prevents loops from being formed when switches or bridges are interconnected via multiple paths.  It does this by creating a logical tree structure that spans all the devices in the network, and disabling or blocking the links that are not part of the tree, leaving a single active path between any two devices 3 .

By eliminating loops, a spanning tree protocol also eliminates broadcast storms, as broadcast packets will not be forwarded endlessly along the looped paths.  Instead, broadcast packets will be sent only along the tree structure, reaching each device once and avoiding congestion 3 .

An aggregate route is a route that summarizes multiple more specific routes into a single route advertisement. For example, an aggregate route to 10.0.0.0/8 can represent many routes to 10.x.x.x/24 subnets. An aggregate route has several purposes, such as:

To decrease the number of route advertisements: By consolidating multiple routes into one, an aggregate route reduces the size of the routing table and the amount of routing updates that need to be exchanged between routers. This can improve the scalability and efficiency of the network12.

To hide internal routes from external peers: By advertising only the aggregate route and not the more specific routes, an aggregate route can provide a level of abstraction and security for the internal network topology. This can prevent external peers from knowing the details of the internal routes and avoid potential attacks or misconfigurations13.

The other options are not correct because:

C. To allow external peers to see internal routes: This is the opposite of what an aggregate route does. An aggregate route hides the internal routes from external peers, not exposes them13.

D. To increase the number of route advertisements: This is also the opposite of what an aggregate route does. An aggregate route decreases the number of route advertisements, not increases them12.

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 .

The exhibit shows the configuration of RSTP on EX-4, which has the command  force-version stp .  This command forces the switch to use the legacy STP protocol instead of RSTP, even though the switch supports RSTP 1 .  This means that EX-4 will not be able to take advantage of the faster convergence and enhanced features of RSTP, such as edge ports, link type, and proposal/agreement sequence 2 .

The other switches in the network are likely to be running RSTP, as it is the default protocol for EX Series switches 3 . Therefore, there will be a compatibility issue between EX-4 and the other switches, which will result in longer convergence times and suboptimal performance.  The switch will also generate a warning message that says “Warning: STP version mismatch with neighbor” when it receives a BPDU from a RSTP neighbor 1 .

To solve this problem, the force-version command must be removed from EX-4, so that it can run RSTP natively and interoperate with the other switches in the network. This will enable faster convergence and better stability for the network topology.  To remove the command, you can use the  delete protocols rstp force-version  command in configuration mode 1 .

In OSPF, the state of the neighbor relationship is determined by the exchange of OSPF packets between routers 1 .  The state “2Way” as shown in the exhibit indicates that bi-directional communication has been established between the two OSPF routers 1 .  This is the normal state for a neighbor that is not the Designated Router (DR) or Backup Designated Router (BDR) on a broadcast, non-broadcast multi-access (NBMA), or point-to-multipoint network 1 .  These neighbors are often referred to as " DRothers " 1 . Therefore, option B is correct.

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]

 A firewall filter is a Junos security solution to filter or control traffic at the data plane as they enter or exit an interface 1 .  A firewall filter consists of one or more terms, each with a set of conditions and actions 2 .  The device evaluates every packet against the firewall filter terms in the order they are defined, and performs the actions specified in the first term that matches the packet 3 .  If no term matches the packet, the device discards the packet by default 3 .

In the exhibit, the firewall filter  mac-address  is applied to the  family ethernet-switching  and involves filtering MAC addresses. There are two terms,  term one  and  term two , each with different conditions and actions. The  from  statement specifies the match conditions, and the  then  statement specifies the actions.  If the  from  statement is omitted, all packets are considered to match and the actions in the  then  statement are taken 2 .  If the  then  statement is omitted, the packets that match the conditions in the  from  statement are accepted by default 2 .

Term one  logs traffic from a specific source MAC address  88:05:00:29:3c:de/48 .  The  log  action is a nonterminating action, which means that the device continues to evaluate the packet against the remaining terms in the filter 2 . Therefore, traffic that matches the  from  statement in term one is not discarded, and option A is incorrect.

Term two  accepts all other traffic not specified in term one.  The  then accept  action is a terminating action, which means that the device stops evaluating the packet against the filter and forwards the packet 2 . Therefore, all traffic not matching the  from  statement in term one is accepted by term two, and option D is correct.

Term two  does not have a  from  statement, which means that all packets are considered to match this term. Therefore, traffic matching the  from  statement in term two is not logged, and option B is incorrect.

Term one  does not have a  then  statement other than the  log  action, which means that the packets that match the  from  statement are accepted by default. Therefore, traffic that matches the  from  statement in term one is accepted, and option C is correct.