Most Recent Juniper JN0-280 Exam Questions & Answers

An IRB (Integrated Routing and Bridging) interface provides routing functionality between VLANs at Layer 3, allowing devices in different VLANs to communicate with each other.

Step-by-Step Breakdown:

IRB Functionality:

The IRB interface enables routing between different VLANs by acting as a Layer 3 gateway. Traffic within the same VLAN is handled by Layer 2 switching, while traffic between VLANs is routed through the IRB interface.

Layer 3 Routing Between VLANs:

Each VLAN can be assigned an IP address on the IRB interface, which allows traffic to flow between VLANs based on Layer 3 IP routing.

Juniper Reference:

IRB Interface Configuration: Juniper supports IRB for inter-VLAN routing on devices like the EX and QFX series switches, facilitating Layer 3 communication in data centers.

To configure aggregated Ethernet (AE) interfaces on a Junos device, the configuration is done under the [edit chassis] hierarchy.

Step-by-Step Breakdown:

Chassis Configuration:

The chassis configuration is responsible for enabling the hardware to support Link Aggregation Groups (LAGs), allowing multiple physical interfaces to be bundled into a single logical interface for load balancing and redundancy.

Command Example:

set chassis aggregated-devices ethernet device-count <number>

This command enables a specific number of aggregated Ethernet interfaces on the device.

Juniper Reference:

LAG Configuration in Junos: The chassis hierarchy is used to allocate and manage hardware resources for aggregated Ethernet interfaces in Juniper devices.

In the exhibit, the BGP routes are marked as hidden. This typically happens when the routes are not considered valid for use, but they remain in the routing table for reference. One common reason for BGP routes being hidden is that the next hop for these routes is unreachable.

Step-by-Step Breakdown:

BGP Next Hop:

In BGP, when a route is received from a neighbor, the next hop is the IP address that must be reachable for the route to be used. If the next hop is unreachable (i.e., the router cannot find a path to the next-hop IP), the route is marked as hidden.

Analyzing the Exhibit:

The exhibit shows that the BGP next hop for all hidden routes is 10.4.4.4. If this IP is unreachable, the BGP routes from that neighbor will not be considered valid, even though they appear in the routing table.

Verification:

Use the command show route 10.4.4.4 to check if the next-hop IP is reachable.

If the next-hop is not reachable, the BGP routes will be hidden. Resolving the next-hop reachability issue (e.g., fixing an IGP route or an interface) will allow the BGP routes to become active.

Juniper Reference:

Junos Command: show route hidden displays routes that are not considered for forwarding.

Troubleshooting: Check the next hop reachability for hidden BGP routes using show route <next-hop>.

An aggregate route is a summarized route that is created by combining multiple specific routes into a single, broader route. In Junos OS, when an aggregate route is configured, its default next hop is set to reject.

Step-by-Step Explanation:

Aggregate Route:

Aggregate routes are used to reduce the size of routing tables by representing a collection of more specific routes with a single summary route. They help improve routing efficiency and scalability, especially in large networks.

Default Next Hop Behavior:

When you configure an aggregate route in Junos OS, it has a reject next hop by default.

The reject next hop means that if a packet matches the aggregate route but there is no more specific route in the routing table for that destination, the packet will be discarded, and an ICMP 'destination unreachable' message is sent to the source.

This behavior helps to prevent routing loops and ensures that traffic isn't forwarded to destinations for which there is no valid route.

Modifying Next Hop:

If needed, the next hop behavior of an aggregate route can be changed to discard (which silently drops the packet) or to another specific next hop. However, by default, the next hop is set to reject.

Juniper Reference:

Junos Command: set routing-options aggregate route <route> reject to configure an aggregate route with a reject next hop.

Verification: Use show route to verify the presence and behavior of aggregate routes.

To display the mapping between VLAN IDs and ports on a Juniper switch, the show vlans command is used.

Step-by-Step Breakdown:

VLAN Information:

The show vlans command displays detailed information about VLAN configurations, including the VLAN ID, associated interfaces (ports), and VLAN membership.

Command Example:

show vlans

This command will provide an output listing each VLAN, its ID, and the interfaces associated with the VLAN, enabling network engineers to quickly verify VLAN to port mappings.

Juniper Reference:

VLAN Verification: Use the show vlans command to verify which VLANs are configured on the switch and the ports that are members of those VLANs.