Use of BROADCAST (B) flag in dhcp...

re: Use of BROADCAST (B) flag in dhcp...

Jeremy Jensen — Wed, 14 Feb 2007 21:02:40 GMT

Is there any reason why the broadcast flag was set to be enabled by default in Vista? I've found some of the major DHCP server vendors (Cisco in particular) do not support it. As such, Vista doesn't work with them without a registry edit. It seems to me that every major DHCP server on the market is capable of unicast but some don't implement the multicast. Wouldn't it be better to have this flag disabled by default then for maximum compatability? Is there some benefit to having it enabled that I've overlooked?

re: Use of BROADCAST (B) flag in dhcp...

Roger Jardine — Tue, 20 Mar 2007 18:40:32 GMT

Is this flag also the same in the version of WinPE that is used in the WDS installation of Vista?

I've found that whilst DHCP at PXE boot and with XP and Vista work just as expected, the version of WinPE used by WDS is not accepting what appear to be perfectly valid DHCP offer packets.

There is some subtle difference that is escaping me here...

re: Use of BROADCAST (B) flag in dhcp...

Rolf Schloemer — Wed, 21 Mar 2007 17:35:25 GMT

Hi Govind,

RFC1542, in sections 3.1.1 and 4.1.2, states that the broadcast flag was introduced as a workaround for old implementations (i.e., old in 1993), and that dhcp servers SHOULD (not MUST!) comply with that flag.

So, does that mean Vista will also accept a unicast offer as a) it's a current OS and b) cannot rely on the server to actually broadcast the offer?

Kind regards,

Rolf

re: Use of BROADCAST (B) flag in dhcp...

teamdhcp — Thu, 29 Mar 2007 08:12:30 GMT

Roger,

WinPE team has seen this happen on machines with NForce NICs that don’t have the latest firmware… in that case, updating the firmware fixes the problem.

Thanks,

Govind

re: Use of BROADCAST (B) flag in dhcp...

Eben van Ellewee — Mon, 23 Apr 2007 12:04:41 GMT

We have about 50 Vista Business machines currently deployed in our company. Funny enought these machines are being used by Microsoft Licensing Experts taking calls....

The problem that we have is that the machines all of a sudden stopped getting IP addresses through DHCP. If you plug in an XP machine it gets it straight away. So what we had to do is set the flag to 0 for it to get an IP. This fix was supposed to be for non-microsoft and some wireless routers... our DHCP servers are up to date Windows 2003 servers... Any comment on that?

re: Use of BROADCAST (B) flag in dhcp...

Rob — Fri, 27 Jul 2007 23:12:41 GMT

I have a newer cisco router, and when I try to get a dhcp address from it (have not changed any settings) I do not add the address to my connection.

When I sniff this exchange, I see that I send the discover with the broadcast flag set, and then I get the offer, with the Your address field set, since its a new binding. Next I send the request for that address back to the router, and the router sends the ack back to me.

At this point, I look in the router, using "show ip dhcp binding" and I see this device in the database, but the Vista client (thinkpad laptop in my lab) does not show this as its IPV4 address. Why does this not work the way it should. I look at the ack from the router, versus when I do the same with a windows dhcp server, and there is not difference in the packets, other than the network they are associated with, and in one case, the vista machine accepts it and in the other it does not.

I let this sit for 10 minutes and never got a usable address (note that at the beginning, I sent a dhcp request, not discover, because I already had a cached ip address for the other subnet I was testing with that the PC had used. I also tried rebooting the vista pc, but still no dice with the cisco router.

Looking at the captures I have, this is clearly a MSFT issue that needs to be properly and publicly addressed and fixed.

[MSFT] If the packets were exactly identical, then the client would have accepted either IP address. The probable cause of the behaviour you are seeing is that one of the options in the ACK message sent by the router must be incorrectly formatted wrt the RFC. This may be causing the client to consider the message as being misformed and drop the ACK message for security reasons.

re: Use of BROADCAST (B) flag in dhcp...

Chris Carday — Wed, 05 Sep 2007 09:53:38 GMT

This toggle stuff isn't working. Is this an upcoming feature or already pushed out in an update?

My Vista DHCP client isn't reversing the flag & retrying when DHCP doesn't succeed.

Thx,

ccarday@yahoo.com

re: Use of BROADCAST (B) flag in dhcp...

frustrated sysadmin — Fri, 28 Sep 2007 04:19:38 GMT

I ran into this today with a client's desktop. What is the rationale for using a long deprecated feature?

re: Use of BROADCAST (B) flag in dhcp...

Kalmi — Sun, 30 Mar 2008 22:40:15 GMT

I have heard that SP1 fixes the toggle thing, is it true?

re: Use of BROADCAST (B) flag in dhcp...

H Berg — Mon, 01 Sep 2008 02:01:06 GMT

it's been said many times already... work ariounds are not good, we need fixes, a form of detetion of the problem, and self-crrection, not a regisyry edit, and when I buy a new router , fix it agian. this mindless resolution of quick fixes represnts a mentality of the new computer age. make problem goi away, instant gratification.. how about the senior approach.. fix the problem so it never ever happerns again. for anyone who is "up to date" on their fixes. as for 'if it aint broke dont fix it".. how about if i have a problem, it's a new one...rather than reinvinting the same round wheel.

re: Use of BROADCAST (B) flag in dhcp...

Harold — Thu, 04 Sep 2008 08:38:26 GMT

I'm a perfetionist.. is my ISP wrong in not corrceting the firmware in themodem.router they support? or is M/S willing to put out a realfix, rather than a procedure to set the flkag in the registry so it works for eeryone correctly, defined as : never getting the msg about "public/network seeking, blah blah".

I would prefer the isp fix the router and everyone fix their s/w and h/wm but realistically, couldn't M/S team just bite the bullit, and make the change for everyone a transoarent one, I for one am not happy to get into registry edits. p.s. can u answerr these quetsions above as well. please.

re: Use of BROADCAST (B) flag in dhcp...

Harold — Sat, 06 Sep 2008 06:41:12 GMT

u have a typo above..

realy agent has to sent reply to broadcast address.

should be

RELAY agent... has to SEND...

p.s. can u publish an UPDATE that adds & sets this flag for all my "connections" , so I don't have to use REGEDIT, please?

re: Use of BROADCAST (B) flag in dhcp...

teamdhcp — Mon, 08 Sep 2008 16:31:59 GMT

Hi H Berg,

Yes we are already working towards such fix which will be kind of self –correction. I will let you know if the fix will be done for Vista and Vista SP1.

Thanks

Ranu

re: Use of BROADCAST (B) flag in dhcp...

teamdhcp — Mon, 08 Sep 2008 16:34:06 GMT

Hi Harold,

Yes we are already working towards such fix which will be kind of self –correction. I will let you know if the fix will be done for Vista and Vista SP1.

Thanks

Ranu

re: Use of BROADCAST (B) flag in dhcp...

teamdhcp — Mon, 08 Sep 2008 17:04:29 GMT

hi Harold,

Made the correction. Thanks for pointing it out. Also are you interested in some tool which will set the toggle bit or the broadcast bit for all interfaces? Please clarify that.

Thanks

Ranu

re: Use of BROADCAST (B) flag in dhcp...

Ben C — Wed, 08 Oct 2008 01:03:33 GMT

When will this issue be resolved. We are continuing to have problems with users at our hotspot's that use Vista. This is costing us a ton in user support costs, with people calling in complaining they aren't able to browse, only to see that they are not picking up an IP from our DHCP server.

re: Use of BROADCAST (B) flag in dhcp...

Sameer N. Mirza — Wed, 15 Oct 2008 10:13:30 GMT

Ben,

as of now this particular fix that toggles automatically without having to set any registry (the one Ranu is talking about) is not planned in Vista. but since you mention that its costing a lot for you then we might consider fixing it. The fixes is shipped OSs happen on a case by case basis which means you cantact PSS and present your business case and based on the impact, workaround and other factors we will take a decision to fix it.

Also in your case the cost seems to be with the support that you provide to your customers so the best bet for you would be to get a redist right on this reg-key based hotfix and distribute it among all your customers, so that they have it by default instead of having to call you and being asked to download this. For this also please get in touch with PSS and they will help you out.