RE: Problem when WinXP firewall is activated (d oes not reply to ping)

>>>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.
>> 
>> 
>> I'm going to check if WinXP does the arping check.

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.


So it seems that Windows XP does an ARP check before using an IP address.
I'll check that with Wireshark on Monday.

>> But the other problem with a SOHO including a DHCP server is that a SOHO 
>> is often rebooted (because the user changed settings which require a 
>> reboot, because of a power failure,...).
>> 
>> So each time it reboots, the lease file is cleared.

>Which is a bug in the SOHO. Assuming by SOHO you mean WRT-54G-class 
>stuff, then you might like to consider moving to DD-WRT. I worked with 
>them to add hooks into dnsmasq so that the lease file can be stored in 
>the non-volatile RAM and not trashed on a reboot. You might also like to
>consider asking the developers of your current firmware to implement the
>same thing.

Could you give me pointers on how to do that?
Is it always safe to reload an old lease file on reboot?

>> 
>> I have the issue only in this case: the SOHO reboots, the WinXP PC 
>> (firewall enabled) has 192.168.1.20, the Linux PC also has 192.168.1.20, 
>> and in the lease file of dnsmasq, 192.168.1.20 corresponds to the MAC 
>> address of the WinXP PC.

>That does look like WinXP might be broken: I'd be interested in the 
>results of your tests.

Again, I'll have to check with Wireshark on Monday. Why do you think it's
WinXP the problem?

--Raphael