Dhcpd versus Windows Vista

Carl Karsten carl at personnelware.com
Wed Mar 14 13:57:04 UTC 2007

A.J. Werkman wrote:
> At 18:00 12-03-2007, you wrote:
>> Koos,
>> I don't think your problem and the knowledge base entry are related.
>> The KB article describes a problem where either the DHCP server or 
>> something in
>> the network between the client and the server (like a router or a switch) 
>> blocks
>> the DHCP packet from the client because the broadcast flag is set in Vista.
>> However, since the server is actually issuing a lease to the client, this is
>> probably not it.
>> You point out that everything works when you open the firewall. Badly 
>> configured
>> firewalls are often a source of problems for DHCP. My recommendation would 
>> be to
>> use Google, and try to find another user with a similar setup and a solution.
>> Failing that, most firewalls have some documentation of some kind. ;)
> I think I have to redescribe this a bit.
> What I call Firewall is actually a linux machine with dual nic. On one side 
> I have a public IP subnet on the other side I have a private IP subnet in 
> the 172.16.x.x range. On this machine I have port forwarding turned off. 
> Furthermore I have a complete ACCEPT entry in the iptables list for the 
> private-side NIC. So this should not interfere with DHCP packets.
> Btw this machine is also doing the DHCP. I don't have any other DHCP 
> "source" on the subnet. If I use linux or XP on the client hardware there 
> is no problem with the DHCP. The machine accepts a lease just as expected. 
> Only a vista installation does not accept the lease. Only if I configure 
> NAT on the linux machine, Vista starts to accept DHCP leases. Also if I 
> replug this client to the public side of the network, where the same isc 
> DHCP-server on the linux machine hands of public IP-addresses I do not see 
> any DHCP problems.
> I also used different hardware for the client to verify. And I do reproduce 
> the same behaviour as describe above. In my opinion this rules out hardware 
> problems. So at the moment, the only thing I can think of, is that Vista 
> itself acts strange if it can not reache mother Microsoft directly 
> (although this should be irrelevant in the DHCP process) or it is the 
> combination Vista/DHCP server that produces the problem. At the moment I am 
> out of ideas, how to debug this problem further.

Use the Wireshark packet sniffer. report the difference between "works" and 
"doesn't work"

Carl K

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