[Dnsmasq-discuss] Problem when WinXP firewall is activated (does not reply to ping)

Raphaël HUCK raphael.huck at efixo.com
Fri Dec 1 17:41:02 GMT 2006

According to 

DHCP client computers running Windows 2000 or Windows XP that obtain an 
IP address use a gratuitous ARP request to perform client-based conflict 
detection before completing configuration and use of a server offered IP 
address. If the DHCP client detects a conflict, it will send a DHCP 
decline message (DHCPDECLINE) to the server.

If your network includes legacy DHCP clients (clients running a version 
of Windows earlier than Windows 2000), you can use server-side conflict 
detection provided by the DHCP Server service under specific 
circumstances. For example, this feature might be useful during failure 
recovery when scopes are deleted and recreated.


Rune Kock wrote:
> On 12/1/06, Raphaël HUCK <raphael.huck at efixo.com> wrote:
>> There is a problem when the firewall of Windows XP is activated, as it
>> does not reply to ping, and dnsmasq checks with ping whether an IP
>> address is already attributed before giving it to someone.
>> As Windows XP doesn't reply to ping when its firewall is activated,
>> dnsmasq thinks the address isn't in use, and gives it to someone else.
> Back in July, when I asked about using arping rather than ping, Simon 
> replied:
>> Interestingly DHCP clients do the address-in-use check too, and since
>> the client only needs to check the local network, it does use ARP.
> As I understand it, the client should try an arping before using the
> address it has been given by the server.
> The interesting question is whether WinXP actually implements this
> arping.  If Windows follows the specification on this, there should be
> no point in the server using arping.
> Rune

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