PING

The PING command is used to test the presence of an active client or server connection.

Ping Request
Usage: PING <server1> [<server2>]
<server1> The server to be pinged.
<server2> An optional second server, used when pinging between two servers.

The server receiving a PING command must respond with a PONG command, using the same server arguments. This is used to verify that the connection is still active and responsive.

(See section 4.6.2 of RFC 1459, 3.7.2 of RFC 2812)