DHCP relay, superscope and laptops

Hi !

I have a DHCP server serving a few seperate subnets. One subnet, which is
out of the superscope, is the one that the DHCP server is in, all the other
subnets are within the superscope. The other subnets connect through a
Level 3 Switch/Router which acts as a DHCP relay agent.

For most of the time everything works fine, until I have to take my laptop
and connect it to different subnets. My laptop has a fixed IP address,
assigned through DHCP as an indefininite reservation of IP address, on the
"primary" subnet, as there are some firewall filters to handle traffic to it
from both the internet, and the other subnets (for management purposes).

When I connect my laptop to any of the other subnets, which are in the
superscope, I get an IP address.

When I then connect it to the next subnet in the superscope, I don't get an
address via DHCP until I delete the assignment from the first subnet.

What I most would like to do is to manually reserve indefinitely one IP
address for my laptop in each subnet, which would be allocated via DHCP when
I connect to that subnet. That way I could set up some filter exceptions
that would only work for that IP address.

Thus, there are two questions:

1. How can I get this fixed IP address in each subnet to be allocated to my
laptop ?

2. How can I get an IP address allocated each time I connect to a subnet
without having to manually delete the first reservation?

Regards,
Palli

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I have a DHCP server serving a few seperate subnets. One subnet, which is
> out of the superscope, is the one that the DHCP server is in, all the
other
> subnets are within the superscope.

Get rid of the Superscope.

> When I connect my laptop to any of the other subnets, which are in the
> superscope, I get an IP address.

Get rid of the Superscope.

> When I then connect it to the next subnet in the superscope, I don't get
an
> address via DHCP until I delete the assignment from the first subnet.

Get rid of the Superscope.

> What I most would like to do is to manually reserve indefinitely one IP
> address for my laptop in each subnet, which would be allocated via DHCP
when
> I connect to that subnet. That way I could set up some filter exceptions
> that would only work for that IP address.

Get rid of the Superscope.

> 1. How can I get this fixed IP address in each subnet to be allocated to
my
> laptop ?

A separate Scope for each subnet. Get rid of the Superscope.

> 2. How can I get an IP address allocated each time I connect to a subnet
> without having to manually delete the first reservation?

A separate Scope for each subnet. Get rid of the Superscope.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Hi !
>
> I have a DHCP server serving a few seperate subnets. One subnet, which is
> out of the superscope,

What's the superscope for?

Superscopes are only needed when the DHCP server offers
addresses to a MULTINET.

Multinet = more than one logical IP subnet on the same cable
segment, or more accurately, the "same broadcast domain."

> ...is the one that the DHCP server is in, all the other
> subnets are within the superscope. The other subnets connect through a
> Level 3 Switch/Router which acts as a DHCP relay agent.

Subnets on differnt cables should be in different scopes and
should NOT have a superscope.

Superscopes are groups of scopes on the same segment,
which is very unusual (not unheard of, but not very common.)

> For most of the time everything works fine, until I have to take my laptop
> and connect it to different subnets. My laptop has a fixed IP address,
> assigned through DHCP as an indefininite reservation of IP address, on the
> "primary" subnet, as there are some firewall filters to handle traffic to
it
> from both the internet, and the other subnets (for management purposes).
>
> When I connect my laptop to any of the other subnets, which are in the
> superscope, I get an IP address.
>
> When I then connect it to the next subnet in the superscope, I don't get
an
> address via DHCP until I delete the assignment from the first subnet.
>
> What I most would like to do is to manually reserve indefinitely one IP
> address for my laptop in each subnet, which would be allocated via DHCP
when
> I connect to that subnet. That way I could set up some filter exceptions
> that would only work for that IP address.
>
> Thus, there are two questions:
>
> 1. How can I get this fixed IP address in each subnet to be allocated to
my
> laptop ?

Start with deleting the superscope.

Before leaving a location you may (optionally) type:

ipconfic /release

Then when you move to a new location you can just type:

ipconfig /renew

(The renew will work without the release, but release is
a good idea if you pool of addresses on the first net is
relatively small -- universities have hundreds of people
leaving one subnet for another after every class, or when
leaving the dorms in the morning, etc.)

> 2. How can I get an IP address allocated each time I connect to a subnet
> without having to manually delete the first reservation?

Modern machines (Win2000+) will usually figure it out if
you REBOOT, but the problem is more irritating with sleep
(hibernate or suspend).

You may have to perform the "ipconfig /renew".

> Superscopes are only needed when the DHCP server offers
> addresses to a MULTINET.

In my case I have a L3 Switch that splits my network in a few distinct VLANs
each of which has it's own subnet. The Switch then acts as a DHCP relay,
relaying DHCP requests to a central DHCP server, which then must offer IP
addresses for different subnets.

I was under the impression that if you had such a setup, you MUST have
superscope(s) set up, right ?

What we did as a workaround, was that we created one superscope for each
VLAN/Subnet and that seems to do the trick, but maybe that's not the way to
go ?

Regards,
Palli


"Herb Martin" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> "Pall Bjornsson" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
>> Hi !
>>
>> I have a DHCP server serving a few seperate subnets. One subnet, which is
>> out of the superscope,
>
> What's the superscope for?
>
> Superscopes are only needed when the DHCP server offers
> addresses to a MULTINET.
>
> Multinet = more than one logical IP subnet on the same cable
> segment, or more accurately, the "same broadcast domain."
>
>> ...is the one that the DHCP server is in, all the other
>> subnets are within the superscope. The other subnets connect through a
>> Level 3 Switch/Router which acts as a DHCP relay agent.
>
> Subnets on differnt cables should be in different scopes and
> should NOT have a superscope.
>
> Superscopes are groups of scopes on the same segment,
> which is very unusual (not unheard of, but not very common.)
>
>> For most of the time everything works fine, until I have to take my
>> laptop
>> and connect it to different subnets. My laptop has a fixed IP address,
>> assigned through DHCP as an indefininite reservation of IP address, on
>> the
>> "primary" subnet, as there are some firewall filters to handle traffic to
> it
>> from both the internet, and the other subnets (for management purposes).
>>
>> When I connect my laptop to any of the other subnets, which are in the
>> superscope, I get an IP address.
>>
>> When I then connect it to the next subnet in the superscope, I don't get
> an
>> address via DHCP until I delete the assignment from the first subnet.
>>
>> What I most would like to do is to manually reserve indefinitely one IP
>> address for my laptop in each subnet, which would be allocated via DHCP
> when
>> I connect to that subnet. That way I could set up some filter exceptions
>> that would only work for that IP address.
>>
>> Thus, there are two questions:
>>
>> 1. How can I get this fixed IP address in each subnet to be allocated to
> my
>> laptop ?
>
> Start with deleting the superscope.
>
> Before leaving a location you may (optionally) type:
>
> ipconfic /release
>
> Then when you move to a new location you can just type:
>
> ipconfig /renew
>
> (The renew will work without the release, but release is
> a good idea if you pool of addresses on the first net is
> relatively small -- universities have hundreds of people
> leaving one subnet for another after every class, or when
> leaving the dorms in the morning, etc.)
>
>> 2. How can I get an IP address allocated each time I connect to a subnet
>> without having to manually delete the first reservation?
>
> Modern machines (Win2000+) will usually figure it out if
> you REBOOT, but the problem is more irritating with sleep
> (hibernate or suspend).
>
> You may have to perform the "ipconfig /renew".
>
>

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:#(E-Mail Removed)...
> > Superscopes are only needed when the DHCP server offers
> > addresses to a MULTINET.
>
> In my case I have a L3 Switch that splits my network in a few distinct
VLANs
> each of which has it's own subnet.

Then each of these should be indistiguishable from
a hardward segment -- each VLAN forms a separate broadcast
domain.

If you only use one IP Subnet range on each VLAN,
you don't have multi-nets and thus don't need Superscopes.

> The Switch then acts as a DHCP relay,
> relaying DHCP requests to a central DHCP server, which then must offer IP
> addresses for different subnets.

It is precisely equivalent to ordinary subnets from
that point of view.

> I was under the impression that if you had such a setup, you MUST have
> superscope(s) set up, right ?

No, because you have no multinets.

Each DHCP server has a NIC on one subnet, and
the other subnets are are in different broadcast domains.

> What we did as a workaround, was that we created one superscope for each
> VLAN/Subnet and that seems to do the trick, but maybe that's not the way
to
> go ?

A Superscope wasn't necessary -- what problem were
you trying to solve?


--
Herb Martin, MCSE, MVP
Accelerated MCSE
http://www.LearnQuick.Com
[phone number on web site]

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> > Superscopes are only needed when the DHCP server offers
> > addresses to a MULTINET.
>
> In my case I have a L3 Switch that splits my network in a few distinct
VLANs

Same here, we use an HP 5300XL

> I was under the impression that if you had such a setup, you MUST have
> superscope(s) set up, right ?

No. No Superscopes. VLANs don't change anything, L3 Switches don't change
anything.

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

>
> "Pall Bjornsson" <(E-Mail Removed)> wrote in message
> news:%(E-Mail Removed)...
> > > Superscopes are only needed when the DHCP server offers
> > > addresses to a MULTINET.
> >
> > In my case I have a L3 Switch that splits my network in a few distinct
> VLANs
>
> Same here, we use an HP 5300XL
>
> > I was under the impression that if you had such a setup, you MUST have
> > superscope(s) set up, right ?
>
> No. No Superscopes. VLANs don't change anything, L3 Switches don't
change
> anything.


What Philip said -- just think of the routing (L3) between
different VLANS as passing through a router.

If effectively creates separate segments/cables -- the advantage it
you the admin get to define these logical segments/cables.

Once done, it is just like a segment with subnet on each one.


You would only need a superscope if you had multiple subnets
on a single segment/VLAN (that is called a "multinet".) You
need a superscope if the DHCP server will hand out addresses
to multiple subnets on such a Multinet.

OK, so to simplify...

I have two subnets A and B, one on each VLAN, connected through a L3 switch
which acts as a DHCP relay to my single DHCP server on subnet A.

A DHCP request from clients on subnet A are no problem as they are local on
the DHCP's server subnet.

A DHCP request from clients on subnet B, pass through the L3 Switch, which
relays them to my DHCP server on subnet A.

How do I then set up those two subents on the DHCP server? Do I just have to
seperate scopes and everyone is happy ever after ?

In the article I read then I needed to declare a superscope for subnet B for
the DHCP server to be able to handle it correctly. Is that not the case ?

Palli



"Herb Martin" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> >
>> "Pall Bjornsson" <(E-Mail Removed)> wrote in message
>> news:%(E-Mail Removed)...
>> > > Superscopes are only needed when the DHCP server offers
>> > > addresses to a MULTINET.
>> >
>> > In my case I have a L3 Switch that splits my network in a few distinct
>> VLANs
>>
>> Same here, we use an HP 5300XL
>>
>> > I was under the impression that if you had such a setup, you MUST have
>> > superscope(s) set up, right ?
>>
>> No. No Superscopes. VLANs don't change anything, L3 Switches don't
> change
>> anything.
>
>
> What Philip said -- just think of the routing (L3) between
> different VLANS as passing through a router.
>
> If effectively creates separate segments/cables -- the advantage it
> you the admin get to define these logical segments/cables.
>
> Once done, it is just like a segment with subnet on each one.
>
>
> You would only need a superscope if you had multiple subnets
> on a single segment/VLAN (that is called a "multinet".) You
> need a superscope if the DHCP server will hand out addresses
> to multiple subnets on such a Multinet.
>
>
>
>

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:%(E-Mail Removed)...
> I have two subnets A and B, one on each VLAN, connected through a L3
switch
> which acts as a DHCP relay to my single DHCP server on subnet A.
>
> A DHCP request from clients on subnet A are no problem as they are local
on
> the DHCP's server subnet.
>
> A DHCP request from clients on subnet B, pass through the L3 Switch, which
> relays them to my DHCP server on subnet A.
>
> How do I then set up those two subents on the DHCP server? Do I just have
to
> seperate scopes and everyone is happy ever after ?

Yep,...that's it

> In the article I read then I needed to declare a superscope for subnet B
for
> the DHCP server to be able to handle it correctly. Is that not the case ?

Not the case. Absolutely not. No Superscopes!

--

Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com

"Pall Bjornsson" <(E-Mail Removed)> wrote in message
news:#(E-Mail Removed)...
> OK, so to simplify...
>
> I have two subnets A and B, one on each VLAN, connected through a L3
switch
> which acts as a DHCP relay to my single DHCP server on subnet A.
>
> A DHCP request from clients on subnet A are no problem as they are local
on
> the DHCP's server subnet.
>
> A DHCP request from clients on subnet B, pass through the L3 Switch, which
> relays them to my DHCP server on subnet A.
>
> How do I then set up those two subents on the DHCP server? Do I just have
to
> seperate scopes and everyone is happy ever after ?

Yes. In DHCP a scope is (effectively) a subnet.

Technically, a scope supplies some portion of the addresses
to a single subnet.

> In the article I read then I needed to declare a superscope for subnet B
for
> the DHCP server to be able to handle it correctly. Is that not the case ?

No.

A superscope would only be necessary if there were two logical
subnes on the single physical VLAN-B (etc.) -- each subnet would
require a scope, but since they are on the same VLAN (same broadcast
domain) they would need to be combined into a superscope.

Your situation is PRECISELY equivalent to the admin with a router
separating two subnets (in regards to DHCP, relaying, and scopes.)

Your VLAN switch just sets up the two broadcast domains electrically
instead of directly physically.