Behavior with clients using "Broadcast Flag"

[Shawn Routhier]

You may wish to check out the ping-check option from the dhcpd.conf man page.
This allows you to disable the ping check.  If you aren't worried about conflicts
it would alleviate your problem.  

Shawn

On Oct 5, 2012, at 3:09 PM, Nicolas C. wrote:

> Hi,
> 
> I'm using dhcpd version 4.1.1 (Debian Squeeze) and I have some Windows Seven clients doing some "discover" instead of "request". This is an example :
> 
> Sep 26 01:19:34 dhcpd: DHCPDISCOVER from 00:1c:c0:fc:f7:24 (VNDLOL65TEE) via 172.20.24.72
> Sep 26 01:19:34 dhcpd: ICMP Echo reply while lease 172.20.24.86 valid.
> Sep 26 01:19:34 dhcpd: if VNDLOL65TEE.domain.com IN TXT "31a956a7940aee9c9191f5c7770adf3ed5" rrset exists and VNDLOL65TEE.domain.com IN A 172.20.24.86 rrset exists delete VNDLOL65TEE.domain.com IN A 172.20.24.86: success.
> Sep 26 01:19:34 dhcpd: if VNDLOL65TEE.domain.com IN A rrset doesn't exist and VNDLOL65TEE.domain.com IN AAAA rrset doesn't exist delete VNDLOL65TEE.domain.com IN TXT "31a956a7940aee9c9191f5c7770adf3ed5": success.
> Sep 26 01:19:34 dhcpd: removed reverse map on 86.24.20.172.in-addr.arpa.
> Sep 26 01:19:34 dhcpd: Abandoning IP address 172.20.24.86: pinged before offer
> 
> I think this behavior is caused by the DHCP "Broadcast flag" introduced by default by windows Vista (to be confirmed) :
> 
> http://blogs.technet.com/b/teamdhcp/archive/2009/02/12/dhcp-broadcast-flag-handling-in-windows-7.aspx
> 
> I'm trying to understand what's happening. The DHCP server :
> 
> - receives a "DHCPDISCOVER", assumes that the client has no IP address but in fact the client is using its currently leased address (172.20.24.86).
> 
> - finds a previous lease with the client hardware address, associated with the IP address 172.20.24.86
> 
> - sends an ICMP message to the IP address before replying to the client
> 
> - gets and ICMP response from the IP address and declares the lease invalid, cleans the DNS
> 
> - assigns another IP address to the client (not displayed in the log).
> 
> Am I right?
> 
> Is there a workaround for this on the server-side, maybe on newer versions of dhcpd?
> 
> Off topic : we've been playing with the registry settings to reproduce / fix this problem and it's not working : the clients keep doing broadcast whatever the settings are and we cannot force a "fresh" install to do broadcat (!!).
> 
> Any help on this would be appreciated, the tech support is blaming the DHCP server :)
> 
> Regards,
> 
> Nicolas
> 
> 
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