What is needed for a ping to be answered?
 

Is there a ping daemon or something?

It uses something called icmp protocol. There is no daemon but this protocol can be blocked by firewalls (including iptables at host level). Many things block icmp so it doesn't always work.

There is a discussion of it here:
http://www.techexams.net/forums/netw...rt-number.html

Ping must be sent. Must be received, the received side has to send reply the origination site has to receive.

Say what? :p

I underthought that.