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I could use some guidance on migrating our Windows 2003 DHCP services to Windows 2008 R2.

We have two buildings:

  • BuildingA contains client ranges x.x.192.x and x.x.193.x, router is x.x.192.1

  • BuildingB contains client ranges x.x.194.x and x.x.195.x, router is x.x.194.1

We currently have four DHCP servers:

  • ServerA hosts range x.x.192.x (also a DC and DNS server)

  • ServerB hosts range x.x.193.x

  • ServerC hosts range x.x.194.x (also a DC and DNS server)

  • ServerD hosts range x.x.195.x (also a DC and DNS server)

Four hosts essentially gives us some pseudo-split-scope fail over. What I'd like to do is consolidate the four existing DHCP servers into our three new Windows 2008 servers, while maintaining some form of fail over. For example, could I do:

  • ServerE hosts range x.x.192.x
  • ServerF hosts range x.x.193.x && x.x.194.x
  • ServerG hosts range x.x.195.x

This way, I have two DHCP servers per building, and I don't require a fourth: I have a valid need for three, but the fourth is seemingly overkill.

Is this even possible? What would you suggest? If there's a better way, I'm very open to suggestion. Thanks in advance.

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  • Where will the three servers be located? Two at one building, one at the other? – SpacemanSpiff Nov 2 '10 at 20:02
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There are two basic techniques here:

1) Split-scope - Some use an 80/20 or 70/30 rule, depends on how many addresses you are working with.

2) Overlapping scopes - You give the full scope to both servers. Windows DHCP will ping an address before issuing it to see if its available, you can add a "delay" to secondary servers so they don't answer for that scope before the primary. This might get messy with client side firewalls blocking ICMP.

If it were my network I'd configure the following:

Server A - Primary DNS Bldg A, Primary DHCP, Full Scopes for Building A
Server B - Secondary DNS Bldg A and Bldg B, Secondary DHCP, Full Scope for Building A with delay, 20% scopes for building B with a smaller delay (take into account WAN latency!).
Server C - Primary DNS Bldg B, Primary DHCP Bldg B 80% of scope.

Keep your DHCP helpers in order.

Tom

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  • You might also consider looking into clustering, if you have shared storage. 2008 R2 was supposed to have DHCP failover without traditional clustering but the RFC wasn't finished so it was dropped from the R2 release. – SpacemanSpiff Nov 2 '10 at 20:37

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