[Mikrotik] Mikrotik DHCP problems with Vista

Chris Gotstein chris at uplogon.com
Tue Jun 24 17:21:03 CDT 2008


We have found this to happen with some routers as well.  Disabling IPv6 
on the client seems to fix the problem.  You do not have to uninstall 
it, just uncheck the box and reboot the machine.  It should then pull 
the ip address.  Not sure if this is the same issue, but it has cleared 
up DHCP related issues with routers in the past.

Chris Gotstein
Sr Network Engineer
UP Logon/Computer Connection UP
500 N Stephenson Ave
Iron Mountain, MI 49801
Phone: 906-774-4847
Fax: 906-774-0335
chris at uplogon.com

David Hulsebus wrote:
> We have a hotspot setup in a hotel and are having issues with vista 
> obtaining leases from the hotspot on a RB192 running 2.945
> 
>  From what I have gleaned from the Mikrotik forums is that the problem 
> is that Microsoft did not follow the DHCP rfc.  Here's the link to the 
> forum discussion.  http://forum.mikrotik.com/viewtopic.php?f=2&t=20979  
> I see that the moderator points folks to 
> http://support.microsoft.com/kb/928233 . It appears Mikrotik has washed 
> their hands of the issue and blames Microsoft for non-compliance.
> 
> I read the rfc and include the pertinant section 4.1 of rfc2131 listed 
> below. The entire rfc is at http://www.ietf.org/rfc/rfc2131.txt
> 
>    Normally, DHCP servers and BOOTP relay agents attempt to deliver
>    DHCPOFFER, DHCPACK and DHCPNAK messages directly to the client using
>    uicast delivery.  The IP destination address (in the IP header) is
>    set to the DHCP 'yiaddr' address and the link-layer destination
>    address is set to the DHCP 'chaddr' address.  Unfortunately, some
>    client implementations are unable to receive such unicast IP
>    datagrams until the implementation has been configured with a valid
>    IP address (leading to a deadlock in which the client's IP address
>    cannot be delivered until the client has been configured with an IP
>    address).
> 
>    A client that cannot receive unicast IP datagrams until its protocol
>    software has been configured with an IP address SHOULD set the
>    BROADCAST bit in the 'flags' field to 1 in any DHCPDISCOVER or
>    DHCPREQUEST messages that client sends.  The BROADCAST bit will
>    provide a hint to the DHCP server and BOOTP relay agent to broadcast
>    any messages to the client on the client's subnet.  A client that can
>    receive unicast IP datagrams before its protocol software has been
>    configured SHOULD clear the BROADCAST bit to 0.  The BOOTP
>    clarifications document discusses the ramifications of the use of the
>    BROADCAST bit [21].
> 
>    A server or relay agent sending or relaying a DHCP message directly
>    to a DHCP client (i.e., not to a relay agent specified in the
>    'giaddr' field) SHOULD examine the BROADCAST bit in the 'flags'
>    field.  If this bit is set to 1, the DHCP message SHOULD be sent as
>    an IP broadcast using an IP broadcast address (preferably 0xffffffff)
>    as the IP destination address and the link-layer broadcast address as
>    the link-layer destination address.  If the BROADCAST bit is cleared
>    to 0, the message SHOULD be sent as an IP unicast to the IP address
>    specified in the 'yiaddr' field and the link-layer address specified
>    in the 'chaddr' field.  If unicasting is not possible, the message
>    MAY be sent as an IP broadcast using an IP broadcast address
>    (preferably 0xffffffff) as the IP destination address and the link-
>    layer broadcast address as the link-layer destination address.
> 
> 
> It appears to me that Mikrotik is incorrect and that the broadcast bit 
> being set to 0 or 1 is indeed a component of  the rfc. Am I reading this 
> correctly? More important has anyone found a resolution?
> 
> Thank you,
> 
> Dave Hulsebus
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