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Need Clarification on Setting up Second DHCP Server for Redundancy

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  #1  
Old 07-03-2007
EdGreen
 
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Need Clarification on Setting up Second DHCP Server for Redundancy

I have one DCHP server with several scopes (corresponding to VLANS). For
redundancy, I want to add an additional DCHP server on the same subnet as the
current DHCP server:

Current DHCP server: DCHPserver1.eg.net [10.99.9.1]
Scopes on DHCPserver1 are currently setup in the following way:
Scope [10.1.0.0] VLAN1 Address Pool 10.1.10.2 10.1.11.254
Scope [10.2.0.0] VLAN2 Address Pool 10.2.10.2 10.2.11.254

I plan on duplicating the scopes exactly on the second DCHP server, and
exclude half of the addresses in each pool (50/50) on each server. Thus, for
Scope [10.1.0.0] VLAN1 , DHCPserver1 would service addresses 10.1.10.2
through 10.1.10.255 and DHCPserver2 would service addresses 10.1.11.0 through
10.1.11.254.

Will this work or do I need to additionally set up superscopes? In DCHP
Best Practices, it is mentioned to setup superscopes to avoid DCHPNAKs. Is
this necessary in my situation?



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  #2  
Old 07-03-2007
Herb Martin
 
Posts: n/a
Re: Need Clarification on Setting up Second DHCP Server for Redundancy


"EdGreen" <EdGreen@discussions.microsoft.com> wrote in message
news:CDD929F3-F1EC-4544-9CF8-7BE293E71A0A@microsoft.com...
>I have one DCHP server with several scopes (corresponding to VLANS). For
> redundancy, I want to add an additional DCHP server on the same subnet as
> the
> current DHCP server:
>
> Current DHCP server: DCHPserver1.eg.net [10.99.9.1]
> Scopes on DHCPserver1 are currently setup in the following way:
> Scope [10.1.0.0] VLAN1 Address Pool 10.1.10.2 - 10.1.11.254
> Scope [10.2.0.0] VLAN2 Address Pool 10.2.10.2 - 10.2.11.254
>
> I plan on duplicating the scopes exactly on the second DCHP server, and


That is correct but not everyone understands it -- so if your "friends" try
to
talk you out of it RESIST.

> exclude half of the addresses in each pool (50/50) on each server. Thus,
> for


Correct. Half is an arbitrary number but makes perfect sense if you wish
each
DHCP server to handle the same (approximate) load. Again, some people have
learned about a SUPPOSED 80/20 "rule" which is no RULE, but merely was
an interesting suggestion in another context, i.e., a context different than
yours.

There is nothing wrong with 70/30 or any other ratio that meets your needs
and
50/50 is usually the most sensible ratio for redundent DHCP servers.

> Scope [10.1.0.0] VLAN1 , DHCPserver1 would service addresses 10.1.10.2
> through 10.1.10.255 and DHCPserver2 would service addresses 10.1.11.0
> through
> 10.1.11.254.


Yes. Also exclude (from both server/scopes) any address in use by a machine
manually, AND on both servers define any RESERVATIONS (with exactly same
entries and options) so that it won't matter which DHCP server gives out the
reservation.

> Will this work


Yes, it will work

> ...or do I need to additionally set up superscopes?


and NO you do not need "superscopes" which are only used for MULTINETS,
that is when you have more than one IP Subnet on the same broadcast domain,
that is on the same physical wire or same VLAN equivalent.

> In DCHP
> Best Practices, it is mentioned to setup superscopes to avoid DCHPNAKs.
> Is
> this necessary in my situation?


No. Where is that reference. It is either wrong or doesn't say what you
think it
says.

The NAKs are prevented by the overlapping scopes on two servers.
Superscopes
are only for two DIFFERENT scopes on the same server which are servicing the
SAME "Broadcast domain".


--
Herb Martin, MCSE, MVP
http://www.LearnQuick.Com
(phone on web site)


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