JN0-102 · Question #100
Which two statements describe the forwarding table in the Junos OS? (Choose two.)
The correct answer is B. The forwarding table stores a subset of information from the routing table. C. Junos devices use the forwarding table to compare incoming packets against existing entries to. The Junos OS forwarding table is a streamlined subset of the routing table, containing only active routes, which the device's Packet Forwarding Engine uses for high-speed packet forwarding decisions.
Question
Which two statements describe the forwarding table in the Junos OS? (Choose two.)
Options
- AThe forwarding table contains all known routes.
- BThe forwarding table stores a subset of information from the routing table.
- CJunos devices use the forwarding table to compare incoming packets against existing entries to
- DIf multiple matches exist, the forwarding table uses the least-specific entry to forward packets toward
How the community answered
(40 responses)- A3% (1)
- B95% (38)
- D3% (1)
Why each option
The Junos OS forwarding table is a streamlined subset of the routing table, containing only active routes, which the device's Packet Forwarding Engine uses for high-speed packet forwarding decisions.
The routing table (RIB) contains all known routes, including inactive ones, while the forwarding table (FIB) contains only the best, active routes optimized for forwarding.
The forwarding table (FIB) in Junos OS is populated from the routing table (RIB) and stores only the active, best routes that have been selected and optimized for rapid lookups, thus representing a subset of the RIB.
Junos devices, specifically their Packet Forwarding Engine (PFE), rely on the forwarding table to perform extremely fast comparisons of incoming packet destination addresses against existing entries to determine the next-hop.
The forwarding table uses the longest prefix match (most-specific entry) to determine the correct next-hop for a packet, not the least-specific entry.
Concept tested: Junos routing vs. forwarding table
Source: https://www.juniper.net/documentation/us/en/software/junos/routing-basics/topics/concept/routing-tables-overview.html
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