Juniper Updated JN0-352 Exam Questions and Answers by roisin

A GRE tunnel's outer, delivery-layer packets are forwarded using the router's ordinary underlay routing table, meaning the tunnel destination address (192.168.0.1 in this case) must itself be resolvable to a physical, non-tunnel next hop for the encapsulated packets to actually leave the router. Before this configuration change, the default route (or some more specific route) presumably pointed toward a real physical next hop, allowing the router to reach 192.168.0.1 and keep the tunnel operational. When the administrator commits a static default route of 0.0.0.0/0 with a next hop of gr-0/0/0, every destination lookup that previously fell back to the default route — including the lookup for the tunnel's own destination address, 192.168.0.1, since no more specific route exists for it — now recurses through the GRE interface itself. This creates a circular dependency: the router needs to route to 192.168.0.1 to keep the tunnel up, but the only route it has to reach 192.168.0.1 now points back into the tunnel that requires 192.168.0.1 to already be reachable, so the interface's next-hop resolution fails and the tunnel drops. This is an entirely valid and common GRE design pitfall rather than any platform restriction; GRE interfaces can be legitimately used as static route next hops, do not require loopback-sourced encapsulation, and do not require a /32 host route to resolve their destination, provided that route does not recursively point back through the tunnel. Reference topics: Junos Enterprise Routing – Tunneling, Route Recursion and GRE Tunnel Destination Resolution.

By default, EBGP sessions are built with the expectation that peers are directly connected at Layer 3, and Junos enforces this by sending EBGP packets with a TTL of 1. When loopback addresses are used as the session endpoints instead of the directly connected physical interface addresses, the resulting IP packets must traverse at least one additional router hop between the two loopbacks, and a TTL of 1 will expire in transit before reaching the remote loopback, causing the TCP handshake — and therefore the BGP session — to fail even though a valid route to the peer's loopback exists. The multihop statement (configured as an EBGP multihop parameter with an accompanying TTL value, most commonly set to 2 for a single intermediate hop) instructs Junos to increase the TTL used for that peer's BGP packets so they survive the extra hop count between loopbacks. This is a mandatory addition any time an EBGP session is deliberately built against non-directly-connected addresses, whereas IBGP sessions, by contrast, do not have this default restriction because IBGP already assumes peers may be multiple hops apart within the same AS. Multipath affects load-balancing across equal-cost paths, damping suppresses flapping routes, and passive controls whether a router waits for the remote peer to initiate the TCP connection — none of these resolve the TTL expiration problem inherent to loopback-based EBGP peering. Reference topics: Junos Enterprise Routing – BGP, Configuring EBGP Multihop Sessions.

Local preference is a well-known, discretionary BGP path attribute carried exclusively in IBGP UPDATE messages, and Junos assigns every route a local preference value of 100 by default whenever a route is received without an explicit LOCAL_PREF value already attached, or when the attribute has not been otherwise modified through routing policy. This default of 100 becomes the implicit baseline against which any administrator-configured local preference adjustments are compared. Because higher local preference values are always preferred over lower ones during BGP best-path selection — and this evaluation happens before AS path length, origin, or MED are ever considered — network engineers commonly use local preference specifically to steer outbound traffic leaving the autonomous system toward a preferred exit peer or upstream provider, by assigning a higher local preference to routes learned from that preferred peer relative to routes learned from alternative peers, making the third statement correct as well. Local preference is explicitly excluded from advertisement to EBGP peers under the BGP specification; it is meaningful only within the boundaries of a single AS and is stripped before a route crosses an AS boundary outward, since a neighboring AS has no reason to trust or honor another organization's internal preference values. A local preference of 0 does not have any special 'drop' semantics in BGP — it is simply the lowest possible numeric preference value and is treated like any other value during comparison, not as a discard instruction. Reference topics: Junos Enterprise Routing – BGP, Local Preference Defaults and Outbound Traffic Engineering.

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 OSPF.