In Junos OS, the Packet Forwarding Engine (PFE) determines the next hop for a packet by performing a lookup in the forwarding table and identifying all valid matches for the destination IP address. When multiple routes encompass the same destination, the router strictly follows the Longest Prefix Match (LPM) rule to select the most specific entry.
For the destination address 10.0.0.9 , the following evaluation occurs based on the exhibit:
10.0.0.0/24 : This route matches, as the address falls within the 10.0.0.0–10.0.0.255 range.
10.0.0.0/26 : This route matches, as the address falls within the 10.0.0.0–10.0.0.63 range.
10.0.0.8/27 : This route matches, as the address falls within the 10.0.0.8–10.0.0.39 range.
10.0.0.4/30 : This route does not match, as its range ends at 10.0.0.7.
Among the matching entries, the prefix lengths are /24, /26, and /27. The longest prefix match is /27 , as it specifies the most granular network segment. Because 10.0.0.8/27 is the most specific match for the destination 10.0.0.9 , the router selects its associated next hop, which is 192.168.2.1 . This deterministic behavior ensures that traffic follows the most precise path calculated by the routing protocols or defined by the administrator, overriding broader routes like the default or summary advertisements.
[Reference: Routing Fundamentals, Longest Prefix Match, Forwarding Table Selection., , ]
