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.

In Junos routing and security contexts, martian addresses are IP prefixes that should not appear as valid, routable sources or destinations on normal interfaces because they are reserved, special-purpose, or otherwise not usable for general unicast forwarding. Treating these as invalid helps protect the control plane and prevents leakage of nonsensical routes into the fabric. This is especially relevant in data center underlays where strict routing hygiene is expected and where improper advertisements can cause blackholing or policy confusion.

The multicast range 224.0.0.0/4 is a classic martian example for unicast routing. These addresses are reserved for multicast and should not be accepted as ordinary unicast sources or carried as typical unicast reachability in an IP fabric. The loopback range 127.0.0.0/8 is also martian on physical networks because it is reserved for host self-reference and must never be forwarded by routers. Seeing it on an interface implies misconfiguration or spoofing.

The prefix 192.0.0.0/24 is reserved for special protocol and IETF assignments and is not intended for general use on public or private networks. As a result, it is commonly treated as martian in routing policy and input validation. By contrast, 172.36.0.0/24 and 198.60.0.0/16 are ordinary globally routable unicast space, so they are not martian by definition.

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.

On broadcast network types in OSPF, such as Ethernet segments, forming a full mesh of adjacencies between every pair of routers would create significant control-plane overhead. Every router would need to maintain neighbor state with every other router, exchange database information redundantly, and flood link-state updates across many parallel adjacencies. This becomes inefficient as the number of routers on the segment grows.

To address this, OSPF elects a Designated Router and a Backup Designated Router. The DR acts as the central point for adjacency formation on that broadcast segment. Instead of each router forming full adjacencies with all others, routers form full adjacencies primarily with the DR and BDR. The DR is responsible for generating and flooding network LSAs that represent the broadcast segment and for coordinating reliable LSA flooding on that segment. This significantly reduces the number of adjacencies and the volume of duplicated database exchange and LSA flooding, which is why option A is correct.

The BDR is a standby control-plane role. It monitors the segment and is prepared to take over the DR function if the DR fails, improving stability and convergence. However, the primary purpose of having DR and BDR is the scaling benefit of reduced adjacency and flooding overhead on broadcast networks.

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 a Virtual 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:

1.     Line Card Role:

o   Member switches acting as line cards provide 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.

2.     Routing Engine Role:

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

3.     Virtual Chassis Roles:

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

o   Backup Routing Engine: Takes over if the master fails.

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

Juniper Reference:

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

In Junos, a static route normally expects its next hop to be directly reachable on a connected interface. When the configured next hop is not directly connected, the router must determine how to reach that next hop using an existing route in the routing table. The resolve feature provides this behavior by allowing Junos to recursively resolve the configured static next hop through another route, such as an IGP learned route, a directly connected route to an intermediate device, or even another static route. Once the system can resolve the next hop to a usable outgoing interface and a final forwarding next hop, the static route becomes active and can be installed in the forwarding table.

This is common in data center environments where you want to point a static route at a loopback address, a service node address, or a next hop that is reachable through the fabric underlay rather than a directly connected subnet. With resolve enabled, the static route’s validity follows the reachability of the recursive path. If the supporting route used for resolution disappears, the static route is withdrawn, helping avoid blackholing traffic toward an unreachable next hop.

The qualified next hop feature is used to define primary and backup next hops with different preferences for the same static route, not to solve indirect reachability by itself. The install and retain options influence route installation and retention behaviors but do not provide recursive resolution of a non-direct next hop.