Juniper JN0-281 Data Center, Associate Exam Practice Test

Answer : D

In Junos OS, routing information is stored in different routing tables depending on the protocol and address family. For IPv6 addresses, the routing table used is inet6.0.

Step-by-Step Explanation:

Routing Tables in Junos:

inet.0: This is the primary routing table for IPv4 unicast routes.

inet6.0: This is the primary routing table for IPv6 unicast routes.

inet.3: This routing table is used for MPLS-related routing.

Other routing tables, like inet.1, inet.2, are used for multicast and other specific purposes.

inet6.0 Routing Table:

When IPv6 is enabled on a Juniper router, all the IPv6 routes are stored in the inet6.0 table. This includes both direct routes (connected networks) and learned routes (from dynamic routing protocols like OSPFv3, BGP, etc.).

Verification:

To view IPv6 routes, the command show route table inet6.0 is used. This will display the contents of the IPv6 routing table, showing the network prefixes, next-hop addresses, and protocol information for each route.

Juniper Reference:

Junos Command: Use show route table inet6.0 to check IPv6 routing entries.

IPv6 Routing: Ensure that the IPv6 protocol is enabled on interfaces and that routing protocols like OSPFv3 or BGP are properly configured for IPv6 traffic handling.

Answer : C

In the exhibit, we see a static route configuration with two possible next hops for the default route (0.0.0.0/0):

next-hop 172.25.20.254 with the default preference of 7.

qualified-next-hop 172.25.20.200 with a preference of 6.

Step-by-Step Breakdown:

Preference Value:

In Junos OS, the preference value is used to determine which route should be preferred in the routing table. The lower the preference value, the higher the priority for the route.

Comparison:

In this case:

The next hop 172.25.20.254 has a preference of 7.

The qualified-next-hop 172.25.20.200 has a preference of 6.

Preferred Next Hop:

Since 172.25.20.200 has a lower preference (6) compared to 172.25.20.254 (7), it will be the preferred next hop in the routing table, assuming both next hops are reachable.

Juniper Reference:

Qualified Next Hop: In Junos, static routes with multiple next-hop options are selected based on the preference value, with the lower value being preferred.

Answer : C

In OSPF (Open Shortest Path First), areas are used to segment a network into smaller, more manageable pieces to improve scalability. By dividing a network into areas, OSPF can reduce the size of the link-state database (LSDB), which helps routers process updates more efficiently.

Step-by-Step Breakdown:

Purpose of OSPF Areas:

OSPF areas allow for hierarchical routing within the OSPF domain. Routers in the same area have identical LSDBs, but routers in different areas do not exchange full link-state information. Instead, they exchange summarized routes, which reduces the LSDB size and CPU/memory usage.

Benefits:

Reducing the LSDB size improves scalability and ensures faster convergence in larger networks. Area 0 is the backbone area, and all other areas must connect to it, forming a hierarchical structure.

Juniper Reference:

OSPF Configuration: Areas in OSPF are configured to optimize network performance by limiting the scope of link-state advertisements (LSAs) to within an area.

Answer : B

In Junos, the default export policy for OSPF is to reject all routes from being exported.

Step-by-Step Breakdown:

Default Export Policy:

By default, OSPF in Junos does not export any routes to other routing protocols or neighbors. This is a safety mechanism to prevent unintended route advertisements.

Custom Export Policies:

If you need to export routes, you must create a custom export policy that explicitly defines which routes to advertise.

Example: You can create an export policy to redistribute static or connected routes into OSPF.

Juniper Reference:

OSPF Export Behavior: In Juniper devices, the default policy for OSPF is to reject route advertisements unless explicitly configured otherwise through custom policies.

Answer : C

A generated route in Junos OS is configured under the [edit routing-options] hierarchy.

Step-by-Step Breakdown:

Generated Routes:

A generated route is created based on the presence of more specific routes in the routing table. It acts as a summary route and is generated when any of its contributing routes are active. This is commonly used to create aggregate routes in OSPF, BGP, or other protocols.

Configuration Hierarchy:

The configuration for generated routes is placed under [edit routing-options], where other static and routing policies are also defined.

Command Example:

set routing-options generate route 10.10.0.0/16

Juniper Reference:

Routing Options: Juniper routers use the routing-options hierarchy to configure generated routes and other static routing behaviors.

Answer : B

In the exhibit, BGP is configured with local AS 65101 and a neighbor at 172.16.1.1 in peer AS 65201. This setup involves two different Autonomous Systems (AS), indicating an External BGP (EBGP) configuration.

Step-by-Step Breakdown:

EBGP vs. IBGP:

EBGP is used between routers in different ASes. In this case, the local AS is 65101 and the peer AS is 65201, meaning the BGP session is EBGP.

IBGP is used between routers within the same AS, which is not applicable here as the AS numbers are different.

BGP Group Configuration:

The configuration does not require a type external parameter because Junos OS automatically recognizes the session as EBGP when the local and peer AS numbers are different.

The BGP session will operate as EBGP, and the configuration will commit successfully.

Juniper Reference:

BGP Configuration: In Juniper, EBGP is automatically recognized when the local and peer AS numbers differ, without needing to specify type external.

Answer : B, C

EVPN-VXLAN is an overlay technology used in data center networks to extend Layer 2 services over a Layer 3 network.

Step-by-Step Breakdown:

BGP Control Plane:

BGP (Border Gateway Protocol) is used as the control plane for EVPN-VXLAN. BGP advertises MAC addresses and IP address reachability information across the VXLAN network, enabling efficient multi-tenant Layer 2 connectivity over a Layer 3 infrastructure.

Encapsulation:

VXLAN (Virtual Extensible LAN) encapsulates Layer 2 frames into Layer 3 packets. This encapsulation allows Layer 2 traffic to be transported across a Layer 3 network, effectively creating a tunnel for Ethernet frames.

Juniper Reference:

EVPN-VXLAN Configuration: Juniper supports EVPN-VXLAN with BGP as the control plane, allowing scalable Layer 2 connectivity over a routed infrastructure in modern data centers.