Free Juniper JN0-280 Practice Exam with Questions & Answers | Set: 2

In the exhibit, we see two next-hop addresses for the default static route (0.0.0.0/0):

The first next hop is172.25.11.254, with no specified preference.

The second next hop is172.25.11.200, with a specified preference of140.

Step-by-Step Breakdown:

Default Static Route Preference:If no preference is explicitly set for a next hop in Junos, it defaults to5for static routes.

Determining Preference:In this case, the next hop172.25.11.254does not have an explicit preference defined, so it will use the default value of5. The second next hop has a preference of140, which is higher,meaning it will only be used if the primary next hop is unavailable.

Juniper Reference:

Static Route Preference: In Junos, the default preference for static routes is5, and this value is applied unless overridden by the preference parameter.

In athree-stage IP fabric(also known as a Clos fabric), traffic between any two points (ingress to egress) in the fabric isonly two hops away.

Step-by-Step Breakdown:

Three-Stage IP Fabric:

Leaf Layer: Leaf switches connect directly to servers and edge devices.

Spine Layer: Spine switches provide connectivity between leaf switches but do not connect to each other directly.

Two-Hop Communication:In this architecture, every leaf switch is connected to every spine switch. Therefore, when a packet enters the fabric via an ingress leaf switch, it is forwarded to a spine switch, which then directs the packet to the correct egress leaf switch. This path always involves exactly two hops:

Ingress leaf → Spine → Egress leaf.

Benefits:This consistent two-hop path ensures predictable latency and makes the network highly scalable while maintaining low complexity.

Juniper Reference:

IP Fabric Architecture: This two-hop property of Clos fabrics is a hallmark of spine-leaf designs, as supported by Juniper's QFX and EX switches in data centers.

When creating aLAG (Link Aggregation Group)in Junos, theduplex settingsandlink speedmust be the same across all member interfaces.

Step-by-Step Breakdown:

LAG Overview:A LAG combines multiple physical interfaces into a single logical interface to increase bandwidth and provide redundancy. All member links must act as a single cohesive unit.

Interface Requirements:

Duplex: All member interfaces must operate in the same duplex mode (either full-duplex or half-duplex). Mismatched duplex settings can cause performance issues, packet drops, or interface errors.

Link Speed: All interfaces in the LAG must have the same link speed (e.g., all interfaces must be 1 Gbps or 10 Gbps). Mismatched speeds would prevent the interfaces from functioning correctly within the LAG.

Configuration and Validation: Ensure that all member interfaces have identical settings before adding them to the LAG. These settings can be checked using the show interfaces command, and the LAG can be configured using:

set interfaces ae0 aggregated-ether-options link-speed 10g

set interfaces ge-0/0/1 ether-options 802.3ad ae0

Juniper Reference:

LAG Configuration: Duplex and link speed must be consistent across member interfaces to ensure proper LAG operation in Juniper devices.

The exhibit shows a BGP peering scenario between three routers:router1androuter2are part of the same AS (AS65000), while theSP routeris in a different AS (AS65101). This indicates anEBGP (External BGP)peering between the SP router and router1, andIBGPbetween router1 androuter2.

Step-by-Step Breakdown:

Next-Hop Behavior in BGP:

IBGP: In IBGP, thenext-hop addressis not modified when advertising routes within the same AS. Thus, when router1 advertises routes learned from router2 to the SP router, it will keep thenext-hop addressof router1, not router2.

EBGP: In EBGP, thenext-hop addressis modified. When router1 receives routes from the SP router, it will advertise them to router2 with thenext-hop addressof router1.

Route Propagation:

Routes received byrouter1fromrouter2will be advertised to the SP router with router1 as the next hop.

Similarly, routes advertised by theSP routerwill be passed on to router2, with router1 remaining as the next hop.

Juniper Reference:

BGP Next-Hop: Juniper's BGP implementations follow standard BGP next-hop behavior, where the next-hop is modified in EBGP but not in IBGP, ensuring proper route advertisement across autonomous systems.

When advertisingOSPF routesintoBGP, the appropriaterouting policyshould be applied as anexport policyin BGP.

Step-by-Step Breakdown:

OSPF to BGP Route Advertisement:Routes learned via OSPF (a dynamic IGP) need to be exported into BGP to be advertised to external BGP peers. In Junos OS, this is done usingexport policies.

Export Policies in BGP:An export policy controls which routes are advertised out of a BGP session. In this scenario, the routing policy must be applied toBGP as an export policyto export the OSPF-learned routes to external BGP peers.

Policy Configuration:Example configuration:

set policy-options policy-statement EXPORT_OSPF term 1 from protocol ospf

set policy-options policy-statement EXPORT_OSPF term 1 then accept

set protocols bgp group export EXPORT_OSPF

This policy ensures that only OSPF routes are exported into BGP.

Juniper Reference:

Routing Policy: Export policies are used in BGP to control route advertisements to peers, including those learned via OSPF.

InIBGP (Internal Border Gateway Protocol), all routers within the same AS (Autonomous System) must have a logical full-mesh topology. This means that every IBGP router must be able to communicate with every other IBGP router directly or indirectly to ensure proper route propagation.

Step-by-Step Breakdown:

Logical Full Mesh:

In an IBGP setup, routers do not re-advertise routes learned from one IBGP peer to another IBGP peer. This rule is in place to prevent routing loops within the AS.

To ensure full route propagation, alogical full meshis required, meaning every IBGP router must peer with every other IBGP router in the AS. This can be done either directly or via route reflection or confederation.

Physical Full Mesh Not Required:The physical topology does not need to be a full mesh, but the BGP peering relationships must form a logical full mesh. Techniques like route reflectors or BGP confederations can reduce the need for manual full-mesh peering.

Juniper Reference:

IBGP Configuration: IBGP logical full mesh requirements can be simplified usingroute reflectorsto avoid the complexity of manually configuring many IBGP peers.

InOSPF (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 thelink-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.

Thesource MAC addressin the Ethernet header is used to populate thebridging table(also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with the ingress port in its MAC address table.

Step-by-Step Breakdown:

Learning Process:When an Ethernet frame arrives on a switch port, the switch looks at thesource MAC addressand adds this MAC address to the MAC table along with the port it was received on. This process is calledMAC learning.

Purpose:The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding.

Juniper Reference:

Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.

In aVirtual Chassis(VC) configuration, multiple Juniper switches are interconnected to form a single logical device. Each member switch in the Virtual Chassis plays a specific role.

Step-by-Step Breakdown:

Line Card Role:

Member switches acting asline cardsprovide additional ports for traffic forwarding but do not perform control or routing functions. These switches depend on the routing engine to handle control-plane tasks.

Routing Engine Role:

A switch in therouting-enginerole is responsible for control-plane operations such as routing protocol management and control of the Virtual Chassis.

Virtual Chassis Roles:

Master Routing Engine: Handles control-plane functions and manages the entire Virtual Chassis.

Backup Routing Engine: Takes over if the master fails.

Line Card: Provides additional ports and handles data-plane operations.

Juniper Reference:

Virtual Chassis: In a five-member Virtual Chassis, multiple switches act asline cards, while one or more switches are designated as therouting engines(master and backup).