dhcpdecline messages

[Simon Hobson]

Hai Tao wrote:

>you are right for host statement.
>   however, when I ping this ip address, no reply received. how can 
>the client find a conflict while I can not ping it? thanks!

"Responds to ping" is not the same as "is using an IP address" - 
unfortunately. Not long ago it was the norm that devices would 
respond to pings, these days, for a number of reasons including abuse 
by virii and some false perception of security, many admins turn this 
off and many devices/OSs default to not responding.

It's a PITA as it makes network troubleshooting a LOT harder.

As David has already said, they device will normally use ARP to 
determine if a device is already using an address. ARP is required 
for IP to work and so cannot be turned off by 'misguided' 
admins/developers.

I think you will find that after attempting to ping the address in 
question, if you then query the arp table ('arp -a' on most unix like 
systems) you will find that there is in fact a mac address listed for 
it.