What command can you enter on a Cisco router so that it can both poll a time server and be polled by a time server?

The `ntp server <ip-address>` command configures the local router as a client that polls the specified server for time, but it does not enable the local router to be polled as a time source by that server.

The `ntp broadcast client` command configures the router to passively listen for NTP broadcast messages, which does not allow it to be polled as a time server.

The `ntp broadcast destination` command configures the router to send NTP broadcast messages, not to receive polls or form a symmetric peer relationship.

The `ntp peer <ip-address>` command establishes a symmetric active peer relationship, allowing the local router to both receive time updates from the specified NTP server and provide time updates to it, enabling bidirectional synchronization.