Juniper JN0-280 Exam Actual Questions

In BGP (Border Gateway Protocol), when evaluating multiple routes to the same destination, the first attribute that is considered is the local preference value. The local preference is a BGP attribute used to influence outbound routing decisions within an Autonomous System (AS).

Step-by-Step Breakdown:

Local Preference:

The local preference attribute is used to determine which path is preferred for traffic leaving the AS. The higher the local preference value, the more preferred the route.

BGP Path Selection:

The BGP path selection process evaluates the following attributes in this order:

Local Preference (higher is preferred)

AS Path (shorter is preferred)

Origin (IGP > EGP > incomplete)

MED (Multi-Exit Discriminator) (lower is preferred)

Juniper Reference:

BGP Path Selection: In Junos, the local preference attribute is the first to be evaluated when determining the best path for outbound traffic.

In Junos OS, the default route preference for a static route is 5. Route preference values are used to determine which route should be installed in the routing table when multiple routes to the same destination are available.

Step-by-Step Breakdown:

Static Route Preference:

A static route, by default, has a preference of 5, making it a highly preferred route. Lower preference values are more preferred in Junos, meaning static routes take precedence over most dynamic routing protocol routes, such as OSPF (preference 10) or BGP (preference 170).

Route Preference:

Route preference is a key factor in the Junos routing decision process. Routes with lower preference values are preferred and installed in the forwarding table.

Juniper Reference:

Static Routes: In Junos, the default preference for static routes is 5, making them more preferred than most dynamic routes.

When creating an IP fabric underlay using OSPF as the routing protocol, consistent interface speeds are important to ensure optimal traffic distribution and utilization of all links.

Step-by-Step Breakdown:

OSPF and Interface Speeds:

OSPF calculates the cost of a link based on its bandwidth. The default cost calculation in OSPF is:

If interface speeds vary significantly, OSPF may choose paths with lower cost (higher bandwidth), resulting in some links being underutilized.

Equal Utilization:

To ensure that all links are equally utilized in an IP fabric, it is recommended to maintain uniform interface speeds across the fabric. This ensures balanced load sharing across all available paths.

Juniper Reference:

IP Fabric with OSPF: Juniper recommends consistent interface speeds to maintain even traffic distribution and optimal link utilization in IP fabric underlay designs.

In legacy hierarchical network design, three key layers are used to create a scalable and structured network:

Step-by-Step Breakdown:

Access Layer:

The access layer is where end devices, such as computers and IP phones, connect to the network. It typically involves switches that provide connectivity for devices at the edge of the network.

Aggregation Layer (Distribution Layer):

The aggregation layer (also called the distribution layer) aggregates traffic from multiple access layer devices and applies policies such as filtering and QoS. It also provides redundancy and load balancing.

Core Layer:

The core layer provides high-speed connectivity between aggregation layer devices and facilitates traffic within the data center or between different network segments.

Juniper Reference:

Legacy Hierarchical Design: Juniper networks often follow the traditional three-layer design (Access, Aggregation, and Core) to ensure scalability and high performance.

Aggregate routes and generated routes are used to create summarized routes in Junos, but they behave differently in terms of forwarding.

Step-by-Step Breakdown:

Aggregate Routes:

An aggregate route summarizes a set of more specific routes, but it does not have a direct forwarding next hop. Instead, it points to the more specific routes for actual packet forwarding.

Generated Routes:

A generated route also summarizes specific routes, but it has a forwarding next hop that is determined based on the availability of contributing routes. The generated route can be used to directly forward traffic.

Juniper Reference:

Aggregate and Generated Routes: In Junos, aggregate routes rely on more specific routes for forwarding, while generated routes can forward traffic directly based on their next-hop information.