In studying for my MCSE (hence posting here), I set
up a three-computer mini-network to play with. The
server is running Windows 2000 Server. The clients
are running Windows 2000 Pro.

My server has two NICs, one going to each client. I
want to use DHCP to serve both clients.

Client 1 can DHCP correctly and works fine. Client 2,
times out.

Here's why: Client 2 broadcasts a DHCP Discover packet
which is received by NIC 2 on the server. The DHCP
server gets the packet and broadcasts the DHCP Offer
packet as required.

BUT... It broadcasts it from NIC 1, not the NIC it
received the Discover on. Thus, it never gets back
to Client 2, but ends up being ignored by Client 1.

Any advice?

William Korvine

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"William Korvine" <korvine@hotmail.com> wrote in message
> My server has two NICs, one going to each client. I
> want to use DHCP to serve both clients.

I'm tempted to just say "Don't multihome Windows DHCP servers". However you
can do it. First make sure the server's adapters are statically set (duh)
then open the DHCP mmc. Click the server. Then right click it and goto
properties. Then the advanced tab then click the bindings button. You can
turn DHCP on and off on those ips.

My guess is that you had your main connection statically defined and the
other obtaining automatically. Then installed DHCP and then subsequently
assigned an address to the second nic. DHCP doesn't notice that unless you
tell it.

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"70-224" <Iggy@the.pop> wrote in
news:zU7O8.672837$kb4.6717255@news.easynews.com:

> "William Korvine" <korvine@hotmail.com> wrote in message
>> My server has two NICs, one going to each client. I
>> want to use DHCP to serve both clients.
>
> I'm tempted to just say "Don't multihome Windows DHCP servers".
> However you can do it. First make sure the server's adapters are
> statically set (duh) then open the DHCP mmc. Click the server. Then
> right click it and goto properties. Then the advanced tab then click
> the bindings button. You can turn DHCP on and off on those ips.
>
> My guess is that you had your main connection statically defined and
> the other obtaining automatically. Then installed DHCP and then
> subsequently assigned an address to the second nic. DHCP doesn't
> notice that unless you tell it.

Thanks very much for the response.

Unfortunately, I did that. Both NICs are statically defined (to
different IPs), and both are enabled in bindings. I doubt the
DHCP server would have received the Discover from Client 2
unless it had been bound. It's just sending the response off
the wrong NIC.

I am using only a single scope; the two clients are not on
separate subnets. Is there any reason why they must be?

Your first advice (don't multihome DHCP servers) is indeed good
advice. I am doing it this way for two reasons. 1, I don't have
a router (and can't aford one). And 2, for the experience. In
attempting to solve this problem, I have learned about DHCP,
DNS, Performance Monitoring, Network Monitoring, and a bunch
of other stuff. MCSE is about being a problem solver.

Thanks again. Any more thoughts?

William Korvine\

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"William Korvine" <korvine@hotmail.com> wrote in message
> Unfortunately, I did that. Both NICs are statically defined (to
> different IPs), and both are enabled in bindings. I doubt the
> DHCP server would have received the Discover from Client 2
> unless it had been bound. It's just sending the response off
> the wrong NIC.

Well I'm not sure it would receive it if unbound either thinking about it.
Ooops sorry.

> I am using only a single scope; the two clients are not on
> separate subnets. Is there any reason why they must be?

Yes there is. And you are seeing the reason. The server is responding to the
request by using the information on it's routing table. The routing table
say if you want to get to Subnet A then use Nic1 (for instance). Doesn't
matter that the broadcast it received came in on Nic2 since Nic2 is also
Subnet A.

> Your first advice (don't multihome DHCP servers) is indeed good
> advice. I am doing it this way for two reasons. 1, I don't have
> a router (and can't aford one). And 2, for the experience. In
> attempting to solve this problem, I have learned about DHCP,
> DNS, Performance Monitoring, Network Monitoring, and a bunch
> of other stuff. MCSE is about being a problem solver.

Tis ok. I realised that you were doing this for learning reasons which is
why I didn't just saying "don't do it". What you need to do is create 2
subnets. Assign a Subnet A address to Nic1 and a Subnet B address to Nic2.
Then create 2 scopes, Scope A with addresses from Subnet A and Scope B with
addresses from Subnet B. That way the machine will know which Nic to use for
replies.

The next problem you'll have is that those two workstations getting
addresses will both be able to talk to the DHCP server but they won't talk
to each other. You'll have to turn the server into a Router (RRAS snap-in).
And that's a whole new subject to enjoy.

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"70-224" <Iggy@the.pop> wrote in
news:5d9O8.950635$Ka4.135148@news.easynews.com:

> "William Korvine" <korvine@hotmail.com> wrote in message
>> Unfortunately, I did that. Both NICs are statically defined (to
>> different IPs), and both are enabled in bindings. I doubt the
>> DHCP server would have received the Discover from Client 2
>> unless it had been bound. It's just sending the response off
>> the wrong NIC.
>
> Well I'm not sure it would receive it if unbound either thinking about
> it. Ooops sorry.
>
>> I am using only a single scope; the two clients are not on
>> separate subnets. Is there any reason why they must be?
>
> Yes there is. And you are seeing the reason. The server is responding
> to the request by using the information on it's routing table. The
> routing table say if you want to get to Subnet A then use Nic1 (for
> instance). Doesn't matter that the broadcast it received came in on
> Nic2 since Nic2 is also Subnet A.
>
>> Your first advice (don't multihome DHCP servers) is indeed good
>> advice. I am doing it this way for two reasons. 1, I don't have
>> a router (and can't aford one). And 2, for the experience. In
>> attempting to solve this problem, I have learned about DHCP,
>> DNS, Performance Monitoring, Network Monitoring, and a bunch
>> of other stuff. MCSE is about being a problem solver.
>
> Tis ok. I realised that you were doing this for learning reasons which
> is why I didn't just saying "don't do it". What you need to do is
> create 2 subnets. Assign a Subnet A address to Nic1 and a Subnet B
> address to Nic2. Then create 2 scopes, Scope A with addresses from
> Subnet A and Scope B with addresses from Subnet B. That way the
> machine will know which Nic to use for replies.
>
> The next problem you'll have is that those two workstations getting
> addresses will both be able to talk to the DHCP server but they won't
> talk to each other. You'll have to turn the server into a Router (RRAS
> snap-in). And that's a whole new subject to enjoy.

Bingo! I see now. Thanks muchly. I'm gonna go give that
a shot now.

William Korvine

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circa Thu, 13 Jun 2002 21:11:59 GMT, in alt.certification.mcse, 70-
224 (Iggy@the.pop) said,

> > My server has two NICs, one going to each client. I
> > want to use DHCP to serve both clients.
>
> I'm tempted to just say "Don't multihome Windows DHCP servers".

There is nothing wrong with multihoming a DHCP server.

> However you
> can do it. First make sure the server's adapters are statically set (duh)
> then open the DHCP mmc. Click the server. Then right click it and goto
> properties. Then the advanced tab then click the bindings button. You can
> turn DHCP on and off on those ips.
>
> My guess is that you had your main connection statically defined and the
> other obtaining automatically. Then installed DHCP and then subsequently
> assigned an address to the second nic. DHCP doesn't notice that unless you
> tell it.

No, actually, Windows 2000's DHCP service will not bind to a NIC that
obtains its IP address via DHCP.

Laura

--
One man's mundane and boring existence is another man's Technicolor.
-Tick, Strange Days

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>Here's why: Client 2 broadcasts a DHCP Discover packet
>which is received by NIC 2 on the server. The DHCP
>server gets the packet and broadcasts the DHCP Offer
>packet as required.
>
>BUT... It broadcasts it from NIC 1, not the NIC it
>received the Discover on. Thus, it never gets back
>to Client 2, but ends up being ignored by Client 1.

How can you be so sure that Client 2 never gets DHCP offer because the offer
comes out of Nic1? What are the symptoms?

If you have two subnets for two NIC cards, the first thing I would check is to
make sure DHCP can assign IP address to both subnets which both NIC cards
reside in. DHCP automatically will assign the IP with same subnet of the NIC
cards unless a rfc 1542 router automatically attaches a subnet packet to the
DHCP client request.

So, make sure your DHCP can assign IP addresses in the subnet which your NIC2
resides in and see what happens.

Jinsoo
MCSE+I, MCDBA, MCSD

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"ILLINI012" <illini012@aol.com> wrote in message
> How can you be so sure that Client 2 never gets DHCP offer because the
offer
> comes out of Nic1? What are the symptoms?

He was sure because he watched the packets going by.

Long and short of it being the problem was cured. He was trying to use the
same subnet on either side of his multihomed DHCP with one scope.

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circa 23 Jun 2002 03:09:23 GMT, in alt.certification.mcse, ILLINI012
(illini012@aol.com) said,

> >BUT... It broadcasts it from NIC 1, not the NIC it
> >received the Discover on. Thus, it never gets back
> >to Client 2, but ends up being ignored by Client 1.
>
> How can you be so sure that Client 2 never gets DHCP offer because the offer
> comes out of Nic1? What are the symptoms?
>
> If you have two subnets for two NIC cards, the first thing I would check is to
> make sure DHCP can assign IP address to both subnets which both NIC cards
> reside in. DHCP automatically will assign the IP with same subnet of the NIC
> cards unless a rfc 1542 router automatically attaches a subnet packet to the
> DHCP client request.
>
> So, make sure your DHCP can assign IP addresses in the subnet which your NIC2
> resides in and see what happens.
>
I'm thinking that the problem is the fact that he only has one scope.

Laura
--
One man's mundane and boring existence is another man's Technicolor.
-Tick, Strange Days

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