helpfor option ping-check

[Julie Xu]

Steve

I think my dynamic pool has some sort of problem, it assigned an address to one user, and for some time, it will assign this address to another machine before first machine lease time out.

I have checked one of case, and both machine do configured to use dhcp server. That is why I thought to use check ping. 

If I do not use check ping, do I have anyway to fix pool problem? Or do I need check something else on the reason?

Any comments will be appreciated

Thanks in advance

Julie

-----Original Message-----
From: dhcp-users-bounces+j.xu=uws.edu.au at lists.isc.org [mailto:dhcp-users-bounces+j.xu=uws.edu.au at lists.isc.org] On Behalf Of Steven Carr
Sent: Thursday, 27 June 2013 8:40 AM
To: Users of ISC DHCP
Subject: Re:

On 26 June 2013 23:21, Julie Xu <J.Xu at uws.edu.au> wrote:
>         1. what will happen if a host with reserve ip (host1, it maybe a printer) required ip address (10.1.72.88) 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.

Steve
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