JN0-683 Sample Questions & Answers

By default, Junos devices perform per-flow load balancing based on a hash of Layer 3 and Layer 4 information. To override this for all traffic and force a round-robin distribution, a policy-statement with the load-balance per-packet action must be created and then applied as an export policy to the forwarding table under [edit routing-options forwarding-table]. This ensures all packets, regardless of flow, are distributed across available ECMP paths.

In an ingress replication model, the source (ingress) leaf VTEP is responsible for creating a copy of the BUM frame for every other remote VTEP participating in that VNI. The list of remote VTEPs to replicate to is built from the EVPN Type 3 Inclusive Multicast Ethernet Tag (IMET) routes advertised by all VTEPs in the fabric for that VNI.

GBP policies are enforced at the ingress VTEP. When a packet from a web server (Tag 10) arrives, the ingress VTEP checks the policy. A rule allowing Tag 10 to communicate with Tag 20 would permit the packet. When a packet from a database server (Tag 20) tries to initiate a connection to a web server (Tag 10), the ingress VTEP for the database server would check its policy and, finding no explicit allow rule, would drop the packet. This allows for stateful-like enforcement in a distributed manner.

In BGP path selection, the LOCAL_PREF attribute is checked before MED, AS-PATH, or router ID, and it is the standard mechanism for influencing outbound path selection within an autonomous system. By setting a higher LOCAL_PREF (e.g., 200) for routes learned via the primary dark fiber link and a lower default value (100) for the backup MPLS link, all outbound traffic from the DCI gateways will prefer the dark fiber path.

When a switch boots in a ZTP environment, it receives its IP address, netmask, and potentially other options from DHCP. However, to reach a TFTP server on a different subnet, it needs a default gateway. If the DHCP server does not provide Option 3 (Router/Default Gateway), the switch will have no route to the TFTP server and the file download will fail. This is a very common ZTP setup issue.

The EVPN Type 1 route is used for mass withdrawal and aliasing in active-active multihoming. All PEs connected to the same Ethernet Segment (identified by a unique ESI) advertise a Type 1 route for that ESI. This allows remote PEs to learn all paths to the segment and perform load balancing (aliasing). It is also used for fast convergence; if a PE loses connectivity to the segment, it withdraws its Type 1 route, signaling remote PEs to stop sending traffic to it.

For high-frequency, low-impact telemetry, Juniper Telemetry Interface (JTI) using UDP as the transport is the ideal choice. UDP is connectionless and has lower overhead than TCP, which is used by gRPC. JTI with native sensors can push data directly from the Packet Forwarding Engine (PFE), minimizing CPU involvement and allowing for very high-frequency data collection suitable for interface and queue statistics.

This feature is known as an Anycast Gateway. Its primary benefit is that a host (server or VM) can use the same default gateway IP address regardless of which leaf switch it is connected to. This enables seamless mobility (e.g., vMotion) across the fabric without requiring any changes to the host's network configuration and ensures that egress traffic is always routed by the local leaf switch, providing optimal forwarding.

This statement is false. A fundamental principle of Clos topologies, whether 3-stage or 5-stage, is that switches at the same layer do not connect to each other. In a 5-stage fabric, leaf switches connect to spine switches within their pod. The spine switches then connect to the super-spine switches, which interconnect the pods. All inter-pod traffic must traverse the spine and super-spine layers.

BFD provides a low-overhead, rapid failure detection mechanism. By establishing BFD sessions from the leaf switches to the service interfaces on both SRX devices, the leaf can detect a failure in milliseconds.

The next-hop-group feature allows you to define a list of next-hops for forwarding. When combined with BFD, the switch will monitor the liveness of each next-hop in the group. If the BFD session to the primary SRX fails, the switch automatically removes it from the forwarding path and starts using the secondary SRX next-hop.