JN0-352 Practice Questions

The described symptom — excessive packet drops specifically attributed to exceeding the MTU on a GRE tunnel carrying full-size video streaming traffic across default-MTU gigabit Ethernet interfaces — is a direct consequence of the 24 bytes of GRE encapsulation overhead pushing packets that were already at or near the standard 1500-byte Ethernet MTU past the physical interface's transmission limit once the outer GRE and IP headers are added. The most durable fix is to proactively increase the physical member interfaces' MTU beyond the 1500-byte default — to 1524 bytes or higher — which provides sufficient headroom to absorb the full GRE encapsulation overhead without ever causing the fully encapsulated packet to exceed the interface's transmission capability, allowing full-size 1500-byte payloads to pass through the tunnel intact and without fragmentation or drops. As a complementary measure, configuring the clear-dont-fragment-bit option on the tunnel or member interfaces instructs Junos to clear the DF (don't fragment) bit on oversized packets rather than dropping them outright when they do exceed the available MTU, allowing the Packet Forwarding Engine to fragment and later reassemble the traffic instead of silently discarding it, which directly addresses the reported packet loss even under transient conditions. Simply raising the MTU only to 1500 bytes fails to account for the 24-byte GRE overhead and would not resolve the underlying oversize condition. Routing the tunnel over a higher-bandwidth link addresses potential congestion but does nothing to correct an MTU-based packet-size violation, which is the root cause explicitly identified in this scenario. Reference topics: Junos Enterprise Routing – Tunneling, GRE MTU Sizing and Fragmentation Handling for High-Throughput Applications.

The metric that OSPF assigns to a destination is visible from two complementary vantage points in Junos. The show route protocol ospf command displays the main routing table filtered to OSPF-learned prefixes, and each entry shows the computed cost alongside the next hop, exactly as it was installed after SPF calculation. The show ospf route command (which accepts filters such as intra-area, inter-area, and extern) presents the OSPF-specific routing table, organized by route type, and explicitly lists the metric column for every intra-area, inter-area, and external route the local router has calculated. Together these two commands give both the RIB-level and the protocol-level view of route cost. By contrast, show ospf database extensive dumps the raw link-state advertisements, where metrics appear only as link-level values buried inside Router or Network LSAs rather than as a resolved route cost, so it is not the direct tool for viewing a route's metric. show ospf interface reports interface operational state, area, and DR/BDR information but does not present a cost or metric field at all in its standard output. Candidates should be comfortable distinguishing the RIB-oriented and protocol-table-oriented verification commands, since JNCIS-ENT scenarios frequently test whether a candidate reaches for the correct show command layer during troubleshooting. Reference topics: Junos Enterprise Routing – OSPF Operation and Verification, Monitoring OSP

F.