A carrier-hotel operator applies a firewall filter to a POP router's transit interface that discards packets from a specific bogon range. After the filter is committed, does the router's routing table change as a result of packets from that range being discarded?
Select an answer to reveal the explanation.
Short Explanation
A firewall filter is strictly about what happens to packets as they cross an interface — it never touches which routes the router knows about. Discarding traffic from a bogon range stops those packets, full stop, but the routing table keeps whatever routes it already learned, untouched.
Full Explanation
A Junos firewall filter operates at the packet-forwarding level: it inspects individual packets against match conditions and applies actions like accept or discard, but it has no mechanism for adding, withdrawing, or otherwise modifying entries in the routing table. Discarding packets from a bogon source range on a transit interface simply means those packets never reach their destination through this router; it has no effect on route learning or advertisement, which is governed entirely by routing policy applied to routing protocols. The claim that routes get automatically withdrawn is a common misconception newcomers make, since filters and policy are frequently confused despite doing fundamentally different jobs — filters touch packets, policy touches routes. Tying route withdrawal to also referencing the filter as an import policy conflates two separate configuration objects; firewall filters and routing policies are distinct structures with different syntax and different points of application, and a filter is never itself an import policy. Making the outcome depend on input versus output direction is also a red herring, since neither direction of a firewall filter has any access to routing-table operations regardless of which way traffic flows. This distinction matters operationally: an engineer troubleshooting unexpected routes should look at routing policy and protocol configuration, not firewall-filter counters, and vice versa for unexpected packet drops. A quick check is comparing 'show route' before and after applying or changing a firewall filter — the table should be identical, since only forwarded packets are affected.