Which command will silently drop a matching packet?

The `no-retain` option prevents a static route from being retained in the routing table when the next-hop interface goes down or is removed, but it does not cause packets to be dropped.

Configuring a static route with the `discard` keyword as the next-hop causes any packets matching that route to be dropped immediately and silently by the router, meaning no ICMP unreachable message is generated or sent back to the source.

The `reject` keyword causes matching packets to be dropped, but it also explicitly sends an ICMP Destination Unreachable message back to the source, which is not a silent drop.

The `passive` keyword for a static route ensures it is installed in the routing table and used for forwarding but not advertised by routing protocols by default; it does not cause packets to be dropped.