Anonymous_User Absent Member.
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setting up multiple vlans with one DHCP server

If I am setting up multiple Subnets on different VLANS to be serviced by one
DHCP server, I understand that a IP helper setup needs to be used in the
router. I am not sure I understand the correlation between the clients and
the DHCPSRVR. How does the server know which IP address from which subnet to
send to the individual clients? Does the DHCPSRVR that is running need to
have an IP address from each of the represented subnets bound to it? Could
someone explain this in more detail? This is what I need to setup over the
Summer so any additional clarification would help me greatly.

Thanks...Roland


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Anonymous_User Absent Member.
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Re: setting up multiple vlans with one DHCP server

Its the job of the router to pass the request from the lan it was made on
to the DHCP server. The information provided by the router's IP helper
is enough to allow the DHCP server to then return the correct information
back.

Due to this process all the DHCP server requires is a single IP address that
can be correctly routed too across the network.

In a VLAN environment you also have the option to set the server up so that
it has IP addresses assigned on each VLAN, so removing the need to
configure the router.

Roger

"Roland lambert" <lamberr@ride.ri.net> wrote in message news:wrcxe.820$nF3.762@prv-forum2.provo.novell.com...
> If I am setting up multiple Subnets on different VLANS to be serviced by one
> DHCP server, I understand that a IP helper setup needs to be used in the
> router. I am not sure I understand the correlation between the clients and
> the DHCPSRVR. How does the server know which IP address from which subnet to
> send to the individual clients? Does the DHCPSRVR that is running need to
> have an IP address from each of the represented subnets bound to it? Could
> someone explain this in more detail? This is what I need to setup over the
> Summer so any additional clarification would help me greatly.
>
> Thanks...Roland
>
>



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Anonymous_User Absent Member.
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Re: setting up multiple vlans with one DHCP server

Roland,

the client sends a DHCP discover packet, which is forwarded from the
router to the dhcp-server. The dhcp-server can see from the incoming
packet, which adress range it has to take the adress from.
There are some more packets (adress offer, acknowledge-packet,...)
send between the dhcp server and the client until the whole
dhcp-converssation is finished.

Joerg
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Anonymous_User Absent Member.
Absent Member.

Re: setting up multiple vlans with one DHCP server

Ok, thanks for the additional info. I am not quite sure I see how the router
is going to know what subnet to assign to based solely on the VLAN. If the
request is for an IP address where is it getting the specific subnet info
from? And how will the DHCP server know what to give out? Will ports on my
switch (cisco) be assigned IP numbers?

Also how will the subnets be setup in the Novell DHCP setup?

I have 9 class C subnets in 4 different buildings

192.168.1.0
3.0
4.0
21.0
22.0
23.0
32.0
33.0
51.0
If you could give me some additional explanation it would be helpful.

Thanks...Roland



"Jörg Schiffer" <Joerg.Schiffer@FernUni-Hagen.de> wrote in message
news:ebqhc1dhbjoo2toju7g2dloctkg4fssjbf@4ax.com...
> Roland,
>
> the client sends a DHCP discover packet, which is forwarded from the
> router to the dhcp-server. The dhcp-server can see from the incoming
> packet, which adress range it has to take the adress from.
> There are some more packets (adress offer, acknowledge-packet,...)
> send between the dhcp server and the client until the whole
> dhcp-converssation is finished.
>
> Joerg



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Anonymous_User Absent Member.
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Re: setting up multiple vlans with one DHCP server

In article <MKAye.2222$cZ.1896@prv-forum2.provo.novell.com>, Roland lambert
wrote:
> I am not quite sure I see how the router
> is going to know what subnet to assign to based solely on the VLAN.
>

When working with VLANs you are working with multiple IP subnets. In order
for those subnets to communicate with each other, there must be one or more
routers to route traffic between the subnets. In order to route traffic
to/from a subnet, the router connecting it to the rest of the world must
have an IP address on that subnet. When a DHCP request is initiated from a
machine on a subnet, the local router hears the request, then sends it to
the DHCP server it is configured to forward to(*). Part of the request
coming from the router includes the router's own IP address, which the DHCP
server then uses to determine which subnet it needs to dole out an address
from.

(*)Each router needs to be told the IP address of the DHCP server it should
forward DHCP requests to(**). This is often referred to as an "IP Helper"
address.

(**)An exception to this is when the DHCP clients and their DHCP server are
on the same subnet, in which case the DHCP requests do not need to be
forwarded.

> If the request is for an IP address where is it [the router] getting
> the specific subnet info from?
>

From the IP address assigned to its own local interface which received the
initial request.

> And how will the DHCP server know what to give out?
>

See above.

> Also how will the subnets be setup in the Novell DHCP setup?
>
> I have 9 class C subnets in 4 different buildings
>

Simply create 9 subnets (192.168.x.0) and a subnet address range within each
of them. In each building, configure the router's IP Helper address as your
DHCP server's IP address.

bd
NSC Volunteer SysOp


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Anonymous_User Absent Member.
Absent Member.

Re: setting up multiple vlans with one DHCP server

There is not much to add to Brad´s comments, but maybe the the basic
steps for dhcp are interesting for you.
1. Create a dhcp-server object
2. Create a subnet-object
3. Create a subnet adress range (SAR)
4. Define options to hand out
5. Define manual assignments (optional)
You can do these steps with the dns/dhcp management console.
5. load dhcpsrvr.nlm
6. Change the clients to dhcp.

Joerg

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Anonymous_User Absent Member.
Absent Member.

Re: setting up multiple vlans with one DHCP server

Thanks Brad and Joerg! It is much clearer to me now. I have worked with DHCP
management console quite a bit but I have not done much with the IPhelper
part. I think I was trying to make it harder than it actually is. That
explanation was what I was looking for, Thanks again...

Roland

"Brad Doster" <bd@NSCSysOps.net> wrote in message
news:VA.000032ab.020761da@nscsysops.net...
> In article <MKAye.2222$cZ.1896@prv-forum2.provo.novell.com>, Roland
> lambert
> wrote:
>> I am not quite sure I see how the router
>> is going to know what subnet to assign to based solely on the VLAN.
>>

> When working with VLANs you are working with multiple IP subnets. In
> order
> for those subnets to communicate with each other, there must be one or
> more
> routers to route traffic between the subnets. In order to route traffic
> to/from a subnet, the router connecting it to the rest of the world must
> have an IP address on that subnet. When a DHCP request is initiated from
> a
> machine on a subnet, the local router hears the request, then sends it to
> the DHCP server it is configured to forward to(*). Part of the request
> coming from the router includes the router's own IP address, which the
> DHCP
> server then uses to determine which subnet it needs to dole out an address
> from.
>
> (*)Each router needs to be told the IP address of the DHCP server it
> should
> forward DHCP requests to(**). This is often referred to as an "IP Helper"
> address.
>
> (**)An exception to this is when the DHCP clients and their DHCP server
> are
> on the same subnet, in which case the DHCP requests do not need to be
> forwarded.
>
>> If the request is for an IP address where is it [the router] getting
>> the specific subnet info from?
>>

> From the IP address assigned to its own local interface which received the
> initial request.
>
>> And how will the DHCP server know what to give out?
>>

> See above.
>
>> Also how will the subnets be setup in the Novell DHCP setup?
>>
>> I have 9 class C subnets in 4 different buildings
>>

> Simply create 9 subnets (192.168.x.0) and a subnet address range within
> each
> of them. In each building, configure the router's IP Helper address as
> your
> DHCP server's IP address.
>
> bd
> NSC Volunteer SysOp
>
>



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Anonymous_User Absent Member.
Absent Member.

Re: setting up multiple vlans with one DHCP server

Glad we could help!

bd
NSC Volunteer SysOp


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Anonymous_User Absent Member.
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Re: setting up multiple vlans with one DHCP server

No problem!

Joerg
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