Meaning of the passive interface command: In common dynamic routing protocols on routers, what does marking an interface as passive actually do?

Introduction / Context:
Most routing daemons support a “passive” setting to control how a specific interface participates in a routing protocol. This is useful on user-facing LANs where you want to advertise the connected network into the protocol but do not want to send hello or periodic update packets that could form neighbor adjacencies with end hosts.

Given Data / Assumptions:

• We are considering distance-vector protocols (for example, RIP, EIGRP in classic update mode) and the general notion across vendors.
• Goal: advertise the network without active neighbor formation on that interface.
• Protocol specifics (like OSPF behavior) may vary, but the exam-style definition focuses on suppressing outbound updates.

Concept / Approach:

Passive on an interface suppresses sending periodic routing updates/hellos out that interface. The router may still receive and process incoming updates (where applicable), and it continues to advertise the connected network via other active interfaces. This prevents unwanted neighbor relationships while keeping route advertisement in the topology database via other links.

Step-by-Step Solution:

Verification / Alternative check:

Show commands (for example, show ip protocols / show run) confirm passive status; packet captures reveal absence of outbound protocol packets on the passive interface.

Why Other Options Are Wrong:

Stopping both send and receive (A) overstates the effect.

Blocking all updates to the router (C/D) applies globally, not per interface, and is not the meaning of the passive flag.

Common Pitfalls:

Assuming passive prevents route learning entirely; confusing protocol nuances (OSPF “passive” prevents adjacency, which effectively stops both directions of hello, but the test definition emphasizes suppression of transmitted updates).

Final Answer:

Stops an interface from sending periodic dynamic updates but not from receiving updates.