Referring to the exhibit, with firewall filter Packet-Filter attached to an interface, if traffic is sent from 192.168.1.1 to 8.8.8.8 for a UDP DNS query, what will happen to the traffic?
A.
The traffic will match term 1 and be forwarded.
B.
The traffic will match the default last term and be forwarded.
C.
The traffic will match the default last term and be discarded.
Junos OS firewall filters operate on a first-match basis, evaluating terms sequentially from top to bottom. In this scenario, a UDP DNS packet (destination port 53) is sent from 192.168.1.1 to 8.8.8.8. Evaluation begins with term 1 , which matches the correct source and destination IP addresses but specifies protocol tcp . Because the actual traffic uses UDP, term 1 is not a match. Evaluation then moves to term 2 . While term 2 correctly identifies protocol udp and port domain (port 53), it requires the source-address to reside within the 192.168.2.0/24 subnet. Since the source is 192.168.1.1 , term 2 also fails to match.
When a packet fails to match any explicitly defined terms in a Junos firewall filter, it is subject to the implicit deny action. This default " last term " is a hardcoded safety mechanism that automatically discards all traffic that has not been explicitly permitted. Consequently, because neither term provides a match for the specific combination of source IP, protocol, and destination port, the DNS query is silently dropped by the Packet Forwarding Engine. This behavior ensures that Junos devices maintain a " deny-by-default " security posture, requiring administrators to define precise permit statements for all required transit or management traffic. Reference: Routing Policy and Firewall Filters, Firewall Filter Evaluation, Implicit Discard.
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