Pong
From Scriptwiki
Used to return a PING command to the sender.
PONG :<string>
When a PING is received, a PONG with the same data must be sent back.
Example
-> blueyonder1.uk.quakenet.org PING 1206662400 <- :blueyonder1.uk.quakenet.org PONG blueyonder1.uk.quakenet.org :1206662400