Juniper JN0-280 Exam Questions

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.

In Junos OS, direct routes are the most preferred routes in the routing table, having the highest priority.

Step-by-Step Breakdown:

Direct Routes:

Direct routes represent networks that are directly connected to the router's interfaces. Since these routes are directly accessible, they are assigned the highest priority and always take precedence over other types of routes.

Preference Values:

Direct routes have a preference of 0, which is the most preferred in Junos. Static routes, OSPF routes, and BGP routes have higher preference values and will only be used if there are no direct routes to the destination.

Juniper Reference:

Direct Route Preference: In Junos, direct routes are always preferred over other routes, ensuring that the router forwards traffic through locally connected networks.