JN0-351 Juniper Enterprise Routing and Switching Specialist (JNCIS-ENT) Free Practice Exam Questions (2026 Updated)

BGP attributes are properties that BGP uses for route advertisement, path selection, and loop prevention 1 .  There are four categories of BGP attributes 1 2 3 :

Well-known mandatory: Must be recognized by all BGP routers, present in all BGP updates, and passed on to other BGP routers 1 2 3 .

Well-known discretionary: Supported by all BGP implementations, and are optionally included in BGP updates 1 .

Optional transitive: May not be supported by all implementations of BGP 1 .

Optional non-transitive: May not be supported by all implementations of BGP 1 .

The well-known mandatory attributes must be supported by all BGP implementations and must be included in every update 1 2 3 .  These include the AS path and next hop attributes 2 3 . Therefore, options A and C are correct.

The BGP attribute that you would use to forward all Internet traffic through the R1 device is the  local preference 1 .

The local preference is an attribute that is used within an autonomous system (AS) and exchanged between iBGP routers 1 .  It is used to select an exit point from the AS 1 .  The path with the highest local preference is preferred 1 .  By setting a higher local preference for the routes received from R1, you can make R1 the preferred exit point for all Internet traffic 1 .

Aggregate routes are used for advertising summarized network prefixes 1 2 .  They help minimize the number of routing tables in an IP network by consolidating selected multiple routes into a single route advertisement 1 .  This approach is in contrast to non-aggregation routing, in which every routing table contains a unique entry for each route 1 .

Therefore, option D is correct. Options A, B, and C are not correct because:

Aggregate routes can be used with both static routing and dynamic routing protocols 1 .

Aggregate routes are not automatically generated for all of the subnets in a routing table.  They need to be manually configured 1 .

Aggregate routes are not always preferred over more specific routes.  The route selection process in Junos OS considers several factors, including route preference and metric, before determining the active route 1 .

https://www.juniper.net/documentation/us/en/software/junos/cli-reference/topics/ref/statement/lsa-refresh-interval-edit-protocols-ospf.html

According to the OSPF protocol, the designated router (DR) is the router that acts as the focal point for exchanging routing information on a multi-access network segment, such as a LAN 1 .  The DR election process is based on the following criteria, in order of precedence 1 :

The router with the highest OSPF priority becomes the DR. The default priority is 1, and a priority of 0 means the router will not participate in the election.

If there is a tie in priority, the router with the highest router ID becomes the DR. The router ID is a 32-bit number that uniquely identifies a router in an OSPF domain. It can be manually configured or automatically derived from the highest IP address of a loopback interface or a physical interface.

If there is a tie in router ID, the router that was first to become an OSPF neighbor becomes the DR.

In your scenario, two routers share the same highest priority and start time. This means that they have equal chances of becoming the DR based on the first and third criteria. Therefore, the second criterion will be used to break the tie, which is the router ID.  The router with the highest router ID will become the DR, and the other router will become the backup designated router (BDR), which is ready to take over the role of DR if it fails 1 .

A route reflector is a BGP router that is allowed to break the iBGP loop avoidance rule and advertise routes received from an iBGP peer to another iBGP peer under specific conditions 1 .  A route reflector can have three types of peerings: EBGP neighbor, IBGP client neighbor, and IBGP non-client neighbor 2 .  A cluster is a group of route reflectors and their clients that are fully meshed 3 .  The cluster ID is a 4-byte value that identifies the route reflector cluster and is carried in the ORIGINATOR_ID attribute of the BGP update message 4 . The cluster ID is used to prevent routing loops among route reflectors and their clients.  If a route reflector receives a route with its own cluster ID, it discards the route 5 . Therefore, the cluster ID is required to prevent routing loops when using route reflectors.

A firewall filter is a configuration that defines the rules that determine whether to forward or discard packets at specific processing points in the packet flow. A firewall filter can also modify the attributes of the packets, such as priority, marking, or logging.  A firewall filter can be applied to various interfaces, protocols, or routing instances on a Juniper device 1 .

A firewall filter has a family attribute, which specifies the type of traffic that the filter can evaluate.  The family attribute can be one of the following: inet, inet6, mpls, vpls, iso, or ethernet-switching 2 . The family inet firewall filter is used to evaluate IPv4 traffic, which is the most common type of Layer 3 traffic on a network.

To create a family inet firewall filter, you need to specify the appropriate match criteria and actions for each term in the filter. The match criteria can include various fields in the IPv4 header, such as source address, destination address, protocol, port number, or DSCP value.  The actions can include accept, discard, reject, count, log, policer, or next term 3 .

To apply a firewall filter to Layer 3 traffic that is being sent between VLANs, you need to apply the filter to the appropriate IRB interface. An IRB interface is an integrated routing and bridging interface that provides Layer 3 functionality for a VLAN on a Juniper device. An IRB interface has an IP address that acts as the default gateway for the hosts in the VLAN.  An IRB interface can also participate in routing protocols and forward packets to other VLANs or networks 4 .

Therefore, option C is correct, because you should create a family inet firewall filter with the appropriate match criteria and actions. Option D is correct, because you should apply the firewall filter to the appropriate IRB interface.

Option A is incorrect, because you should not create a family ethernet-switching firewall filter with the appropriate match criteria and actions. A family ethernet-switching firewall filter is used to evaluate Layer 2 traffic on a Juniper device.  A family ethernet-switching firewall filter can only match on MAC addresses or VLAN IDs, not on IP addresses or protocols 5 .

Option B is incorrect, because you should not apply the firewall filter to the appropriate VLAN. A VLAN is a logical grouping of hosts that share the same broadcast domain on a Layer 2 network. A VLAN does not have an IP address or routing capability.  A firewall filter cannot be applied directly to a VLAN; it must be applied to an interface that belongs to or connects to the VLAN 6 .

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.