[ISC DHCPv6 on Freebsd] Decline Message

Jiri Popelka jpopelka at redhat.com
Wed Nov 3 15:05:07 UTC 2010

Hope this will shed some light on your problem

The client in RHEL6 is patched to send a Decline message when duplicate 
address is detected.
I can send you my patch that makes client send Decline message when 
dhclient-script returns value indicating that DAD failed.

But the next part of this problem is how to make dhclient-script 
discover that DAD failed.
I'm not skilled with other OS besides linux so my patch fixes only 
dhclient-script for linux.
It uses the fact that 'ip addr show' shows 'tentative' flag in address 
info when DAD
is still not complete or failed.

Jiri Popelka
Red Hat, inc.

On 11/03/2010 04:31 AM, frank cui wrote:
> Hi all,
> I'm doing a interoperation test about DHCPv6, and a bit confused on a 
> test case about the DECLINE message.
> Hope Experienced Users can help me solve this problem.
> Here is the details information:
> Server(RHEL6)
>    |
>    |
> --------------------------------------------(2000::/64)
>            |                                   |
>            |                                   |
> Client(FREEBSD8.1)   Reference Host(FREEBSD8.1)
> Software Version:
> Server:dhcp-4.1.1-11.P1
> Client:dhcp-4.1.1-P1
> I manually assign the address 2000::5 to the Reference Host.
> And i make the Server only has the pool address 2000::5.
> After i start the Server and Client DHCP daemon, the Client gets the 
> address 2000::5 and recognizes the address assigned by the server is 
> duplicated, but it doesn't really generate the DECLINE message.
> --------------------------------------------------------------------------------------
> "inet6 2000::5 prefixlen 64 duplicated"(output from ifconfig command 
> on the client)
> And there is also a message on the console:
> "DAD detected duplicate IPv6 address 2000::5: NS in/out=0/1, NA in=1
> DAD complete for 2000::5 - duplicate found
> manual intervention required
> nd6_dad_timer:called with duplicated address 2000::5"
> ---------------------------------------------------------------------------------------
> What do i further need to do to make the client generate the DECLINE 
> message? Thanks a lot in advance.
> Regards,
> Frank

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