nerdexam
Juniper

JN0-102 · Question #261

A packet is evaluated against three user-defined terms within a firewall filter and no match is found. What correctly describes the action the firewall filter will take for this packet?

The correct answer is C. The filter will discard the packet and take no additional action. When a packet is evaluated against a firewall filter and does not match any user-defined terms, the implicit default action is to silently discard the packet. This behavior ensures that unmatching traffic is dropped without notification.

Routing Policy and Firewall Filters

Question

A packet is evaluated against three user-defined terms within a firewall filter and no match is found. What correctly describes the action the firewall filter will take for this packet?

Options

  • AThe filter will permit the packet and take no additional action.
  • BThe filter will reject the packet and send an ICMP message back to the sender.
  • CThe filter will discard the packet and take no additional action.
  • DThe filter will permit the packet and write a log entry to the firewall log.

How the community answered

(45 responses)
  • A
    9% (4)
  • B
    2% (1)
  • C
    87% (39)
  • D
    2% (1)

Why each option

When a packet is evaluated against a firewall filter and does not match any user-defined terms, the implicit default action is to silently discard the packet. This behavior ensures that unmatching traffic is dropped without notification.

AThe filter will permit the packet and take no additional action.

Permitting the packet is not the default action; an explicit 'accept' or 'permit' action must be configured.

BThe filter will reject the packet and send an ICMP message back to the sender.

Rejecting the packet and sending an ICMP message is an explicit action ('reject') that must be configured within a filter term, it is not the default behavior.

CThe filter will discard the packet and take no additional action.Correct

If a packet does not match any user-defined terms in a firewall filter, Junos OS applies an implicit 'discard' action to the packet, effectively dropping it without sending any notification to the sender. This is a security best practice to prevent unsolicited traffic.

DThe filter will permit the packet and write a log entry to the firewall log.

Permitting the packet and logging is not the default action; both 'permit' and 'log' are explicit actions that need to be configured.

Concept tested: Firewall filter default action

Source: https://www.juniper.net/documentation/us/en/software/junos/firewall-filters/topics/topic-map/firewall-filters-overview.html#id-default-actions-for-firewall-filters

Topics

#firewall filters#filter default action#packet filtering

Community Discussion

No community discussion yet for this question.

Sign up to join the discussion
Full JN0-102 Practice