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Backup DHCP Server

Posted on 2016-11-07
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Last Modified: 2016-11-07
Hi Guys,
Currently, I have one server room, we are going to install a second server room at the back of a large building. The main reason for this is, in the event of a fire, we will have a copy of the sql server so we can resume business. all the office pc (2 dozen) will be physically uplugged from the primary network into secondary network.

Since the two database servers will be connected via fiber optics approx 300 feet away, should 1 use a failover DHCP or a seperate DHCP?

You're help is greatly appreciated.
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Question by:S Khan
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by:Lee W, MVP
ID: 41877979
If it's on the same network, use a split scope - half your DHCP addresses are handed out by each server.  If one does down, the other can handle all of the network.  Otherwise, whichever DHCP server answers first provides the address
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by:S Khan
ID: 41877991
Hi Lee, in the event of a fire all the cables will be burnt, so the office pc's will be severed,  so i will be running a separate network. my main focus is to have a backup of the entire database.  I would have to physically connect the office pc to the backup DHCP server.
Do i replicate the DHCP or have a seperate one?

Here is the flow of the primary room
WAN>SonicWALL>DHCP>SQL

Here is the flow of the backup room
Backup WAN > SonicWALL>DHCP>SQL etc.
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by:Lee W, MVP
ID: 41877997
I'm confused - WHY would you run a separate network?  Just have redundant services in two locations - or use Hyper-V replica.  Ditch the sonicwall and use a VM based solution (I prefer Untangle, but PFSense and other third party systems exist that can run as a VM - and since they are running as a VM you can fail them over.
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Expert Comment

by:Mal Osborne
ID: 41878009
I would not use a second DHCP server. When a Windows machine boots, with an existing DHCP lease it attempts to ping the default gateway, and if it can, keeps using that lease. The default Windows DHCP lease is 8 days, leases are renewed once half expired, so clients will be fine with no DHCP server for 4 days.  You could even extend the lease time, maybe to 30 days, giving you 2 weeks grace.

Longer leases can be a problem f you have a lot of devices intermittently in use and not a lot of spare IP addresses. If for instance, a visitor plugs in a laptop, and it gets a lease, that IP cannot be used for 8 days. It is possible to therefore run out of IP addresses.
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by:S Khan
ID: 41878013
In a fire we will loose the entire room, WAN, SonicWALL, Switches. firewall etc, The only thing that remain is a burn out Ethernet cable.
We are planning for worst case scenario.
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by:S Khan
ID: 41878015
also the backup DHCP will be using another gateway.
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Lee W, MVP earned 500 total points
ID: 41878024
In a fire we will loose the entire room, WAN, SonicWALL, Switches. firewall etc, The only thing that remain is a burn out Ethernet cable.
We are planning for worst case scenario.

OK, so I'll repeat...  WHY would you run a separate network?

You don't need a separate network.  If you are convinced that the entire building won't be affected, but just want redundancy, KEEP the same logical network.  There's no reason you've presented that says you can't.

Is there a reason you're not virtualizing?  If you are, is there are a reason you're not replicating?

What your describing sounds like what an inexperienced person might try to design for a disaster - but there are FAR better and less complex ways of doing this.

BTW, the worst case scenario is the entire building burns down.  In which case you need OFF-SITE redundancy - again, something replica can do!
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Author Comment

by:S Khan
ID: 41878042
Actually you're right, same network, different location with a separate WAN.
All the machines are virtual,  Thank you for the guidance.
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