Steven Carr sjcarr at
Wed Jun 26 22:40:09 UTC 2013

On 26 June 2013 23:21, Julie Xu <J.Xu at> wrote:
>         1. what will happen if a host with reserve ip (host1, it maybe a printer) required ip address ( is pingable by reason of itself alive? And what will happened if another machine use the ip and pingable?

You will have an IP conflict and depending on your network environment
both hosts may "battle" for that IP address. The host may reply back
to the DHCP server saying the IP is in use but if it's a fixed-address
then the DHCP server will continue to respond to any DHCP requests for
that host with the fixed-address reservation.

>         2. is the ping-check option can use in subnet? Or even used in pool only?

It is a global option.

All the ping check does is have the DHCP server try to see if that
address is currently in use already. If the ping is responded to then
the DHCP server marks the address as abandoned and moves on to the
next address. Be aware that this does introduce a delay into the
process of issuing a DHCP lease to a host as it has to wait for the
ping to timeout before responding to the DHCPDISCOVER.

If you do not use the ping check then the host will handle this
scenario anyway, when the host receives the DHCPOFFER it will issue an
ARP request asking who has the offered IP address, if another host
responds to the ARP request then the host will respond back to the
DHCP server with a DHCPNAK indicating the IP is already in use.


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