DHCP Superscopes & how to configuring the Router ip helper-address

Here's a post from our Knowledge Base at
http://www.Menkaura.com/Forum/index.php for this and a lot more real
life IT solutions come along to the party. Your Knowledge is important
to us ... sharing if you can.

Regards, Gary


DHCP Considerations and thoughts


What are Superscopes?

By definition a Superscope in a administrative tool for grouping more
than one subnet together.

When a physical LAN has the requirement to accommodate more than one
subnet then Superscopes canbe used
by setting them up via the DHCP MMC.

A physical LAN that has more than one subnet is called a Multinet.

Superscopes canbe empoyed either within the same Routed network or over
diferent Router networks. So for
example a Superscope canbe used to logically group an Engineering
department together as they appear in
different buildings. Here the buidlings are likely to be on different
Routed subnets.


What is an IP Helper-address?

Used on Cisco Routers to act as a source of IP information in terms of
where to send traffic to if a
destination address is not found on the local subnet.

.... and the Cisco definition goes "Defines a helper-address for a
specified address. The helper-address defines
the selective forwarding of UDP broadcasts, including BootP, received
on the interface. The address
argument specifies a destination broadcast or host address to be used
when forwarding such datagrams."


Configuring ip helper-address(s) is undertaken as follows:

ip helper-address 192.168.2.1
or
no ip helper-address 192.168.2.1


Out of the box it will forward the following protocols:

69 TFTP, 67 BOOTP Client, 68 BOOTP Server, 37 Time Protocol, 49 TACACS,
53 DNS, 137 NetBios, 138 NetBios Datagram


Stopping IP helper-address forwarding certain default protocols is
undertaken as follows:

no ip forward-protocol udp 37
no ip forward-protocol udp 49
no ip forward-protocol udp 53
no ip forward-protocol udp 67
no ip forward-protocol udp 68
no ip forward-protocol udp 137
no ip forward-protocol udp 138


Adding other protocols:

Put your ip helper-address command on the interface that receives the
broadcasts, then in global config mode
enter the command as follows as an example:

ip forward-protocol udp 2000

"Gary" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> What are Superscopes?

> By definition a Superscope in a administrative tool for grouping more
> than one subnet together.
> When a physical LAN has the requirement to accommodate more than one
> subnet then Superscopes canbe used
> by setting them up via the DHCP MMC.

The definition isn't wrong,..but it leaves out key information. Superscopes
are used with Multi-Nets, but *not* just multiple Subnets, because having
multiple subnets does not make it a Multi-Net.

> A physical LAN that has more than one subnet is called a Multinet.

It should say "A physical LAN that has more than one subnet... *on the same
wire* ...is called a Multinet."

I know that this was just a quote from textbook material and I'm not blaming
you for it, I've have seen it for a long time,...even back during my Cisco
training,...but the material does need to be corrected to make it more
clear. I see the rusult of it often in the newsgroups a couple times a
month where someone has configured Superscopes for a normal muli-subnet LAN
and then can't figure out why the workstation gets the same IP# over and
over even when it is moved to a different subnet. Remember that a
Superscope makes all the Scopes within it behave as a single unit, therfore
a Client can receive any address from any scope at any time no matter where
it is physically located.

True multi-nets and the use of Superscope that go along with them are very
very rare,...probably because they are so confusing and it is so very very
easy to avoid them in the first place.

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/IS...cessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/t...dance/2004.asp
http://www.microsoft.com/isaserver/t...dance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp
-----------------------------------------------------

Hi Philip

All points taken and received. Thanks for the insight....

Don't suppose you want to post this on the
http://www.Menkaura.com/Forum/index,php site? Your insight would be
much appreciated.

Thanks again...

Gary (MCSE & CCNA)

Phillip Windell wrote:
> "Gary" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
> > What are Superscopes?
>
> > By definition a Superscope in a administrative tool for grouping more
> > than one subnet together.
> > When a physical LAN has the requirement to accommodate more than one
> > subnet then Superscopes canbe used
> > by setting them up via the DHCP MMC.
>
> The definition isn't wrong,..but it leaves out key information. Superscopes
> are used with Multi-Nets, but *not* just multiple Subnets, because having
> multiple subnets does not make it a Multi-Net.
>
> > A physical LAN that has more than one subnet is called a Multinet.
>
> It should say "A physical LAN that has more than one subnet... *on the same
> wire* ...is called a Multinet."
>
> I know that this was just a quote from textbook material and I'm not blaming
> you for it, I've have seen it for a long time,...even back during my Cisco
> training,...but the material does need to be corrected to make it more
> clear. I see the rusult of it often in the newsgroups a couple times a
> month where someone has configured Superscopes for a normal muli-subnet LAN
> and then can't figure out why the workstation gets the same IP# over and
> over even when it is moved to a different subnet. Remember that a
> Superscope makes all the Scopes within it behave as a single unit, therfore
> a Client can receive any address from any scope at any time no matter where
> it is physically located.
>
> True multi-nets and the use of Superscope that go along with them are very
> very rare,...probably because they are so confusing and it is so very very
> easy to avoid them in the first place.
>
> --
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
> -----------------------------------------------------
> Understanding the ISA 2004 Access Rule Processing
> http://www.isaserver.org/articles/IS...cessRules.html
>
> Microsoft Internet Security & Acceleration Server: Guidance
> http://www.microsoft.com/isaserver/t...dance/2004.asp
> http://www.microsoft.com/isaserver/t...dance/2000.asp
>
> Microsoft Internet Security & Acceleration Server: Partners
> http://www.microsoft.com/isaserver/partners/default.asp
> -----------------------------------------------------

"Gary" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> All points taken and received. Thanks for the insight....
>
> Don't suppose you want to post this on the
> http://www.Menkaura.com/Forum/index,php site? Your insight would be
> much appreciated.

I don't know. You're welcome to repeat whatever I say there all you want, I
don't care about that. As far as typing up something "official" with all
the references and such, I don't know if I'd feel up to the task. All it
takes is one little slip of something I say or some little "typo" or some
little overlooked detail, or some obscure "exception to the rule" that I
forgot to mention and I'd have people jumping all over it and I don't think
I need the greif.

It's already bad enough in the newsgroups when my posts are "pure and
pristine" enough.

I do really appreciate you suggesting that. That is a compliment in itself.
I will keep a link to the forums saved and can take a peek in there
sometime.

--
Phillip Windell [MCP, MVP, CCNA]
www.wandtv.com
-----------------------------------------------------
Understanding the ISA 2004 Access Rule Processing
http://www.isaserver.org/articles/IS...cessRules.html

Microsoft Internet Security & Acceleration Server: Guidance
http://www.microsoft.com/isaserver/t...dance/2004.asp
http://www.microsoft.com/isaserver/t...dance/2000.asp

Microsoft Internet Security & Acceleration Server: Partners
http://www.microsoft.com/isaserver/partners/default.asp
-----------------------------------------------------

Thanks Phillip and keep in touch a.

Just got back from a MS Technet evening ... only AD (cold beer and warm
pizza), alas no Superscopes on this occassion.

Regards, Gary


Phillip Windell wrote:
> "Gary" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
> > All points taken and received. Thanks for the insight....
> >
> > Don't suppose you want to post this on the
> > http://www.Menkaura.com/Forum/index,php site? Your insight would be
> > much appreciated.
>
> I don't know. You're welcome to repeat whatever I say there all you want, I
> don't care about that. As far as typing up something "official" with all
> the references and such, I don't know if I'd feel up to the task. All it
> takes is one little slip of something I say or some little "typo" or some
> little overlooked detail, or some obscure "exception to the rule" that I
> forgot to mention and I'd have people jumping all over it and I don't think
> I need the greif.
>
> It's already bad enough in the newsgroups when my posts are "pure and
> pristine" enough.
>
> I do really appreciate you suggesting that. That is a compliment in itself.
> I will keep a link to the forums saved and can take a peek in there
> sometime.
>
> --
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
> -----------------------------------------------------
> Understanding the ISA 2004 Access Rule Processing
> http://www.isaserver.org/articles/IS...cessRules.html
>
> Microsoft Internet Security & Acceleration Server: Guidance
> http://www.microsoft.com/isaserver/t...dance/2004.asp
> http://www.microsoft.com/isaserver/t...dance/2000.asp
>
> Microsoft Internet Security & Acceleration Server: Partners
> http://www.microsoft.com/isaserver/partners/default.asp
> -----------------------------------------------------

Thanks Phillip and keep in touch a.

Just got back from a MS Technet evening ... only AD (cold beer and warm
pizza), alas no Superscopes on this occassion.

Regards, Gary


Phillip Windell wrote:
> "Gary" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
> > All points taken and received. Thanks for the insight....
> >
> > Don't suppose you want to post this on the
> > http://www.Menkaura.com/Forum/index,php site? Your insight would be
> > much appreciated.
>
> I don't know. You're welcome to repeat whatever I say there all you want, I
> don't care about that. As far as typing up something "official" with all
> the references and such, I don't know if I'd feel up to the task. All it
> takes is one little slip of something I say or some little "typo" or some
> little overlooked detail, or some obscure "exception to the rule" that I
> forgot to mention and I'd have people jumping all over it and I don't think
> I need the greif.
>
> It's already bad enough in the newsgroups when my posts are "pure and
> pristine" enough.
>
> I do really appreciate you suggesting that. That is a compliment in itself.
> I will keep a link to the forums saved and can take a peek in there
> sometime.
>
> --
> Phillip Windell [MCP, MVP, CCNA]
> www.wandtv.com
> -----------------------------------------------------
> Understanding the ISA 2004 Access Rule Processing
> http://www.isaserver.org/articles/IS...cessRules.html
>
> Microsoft Internet Security & Acceleration Server: Guidance
> http://www.microsoft.com/isaserver/t...dance/2004.asp
> http://www.microsoft.com/isaserver/t...dance/2000.asp
>
> Microsoft Internet Security & Acceleration Server: Partners
> http://www.microsoft.com/isaserver/partners/default.asp
> -----------------------------------------------------