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I am just wondering if I can run both windows and Ubuntu DHCP/DNS Server in the same LAN. The Present configuration is Windows 2003 Server AD and Ubuntu DHCP n DNS Server with BINDS. I have proposed to upgrade AD to 2008R2 and wanted to have fail over and was wondering "What IF" Scenario for DCHP and DNS.....

Any thoughts and insights are much appreciated

Thanks

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2 Answers 2

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I will give you some thoughts and some links for further reading. Take them with several grains of salt.

DHCP

It is possible to run multiple DHCP servers on the same LAN. However they must not serve the same address pool. Reason is that DHCP is first-come-first-serve. If both machines hand out the same pool, there is a good chance to assign IPs twice.

The easiest way is to split the scope. Say, one server hands out addresses 192.168.0.1-129 and the other 192.168.0.130-254. This way no inconsistencies can arise. This is sort of the "cheap" failover way.

The proper failover method would be, if the servers are aware of each other, so that in the event that one becomes unavailable, the other jumps in. For that to work however, they both need to share a lease-file; the failover partner needs to be aware of which IPs the other one handed out before failure. As far as I know this was introduced as late as Windows Server 2012. The common ISC DHCP server supports this readily; I have seen this in action.

Unfortunately I don't think there is a way to achieve this sort of failover in a heterogeneous environment.

DNS

In principle it is no problem running multiple DNS servers. DNS intrinsically supports replication by assigning master/slave roles.

However with ActiveDirectory things become more complex, as AD relies on DDNS updates from the DHCP. I have now read quite some opinions about this topic ranging from "Not a problem" to "huge clusterfuck". See the links below.

It seems to be no problem to substitute BIND9 for Windows DNS in an AD environment. It also seems to be fine, to run BIND as a secondary along the primary Windows DNS. What I'm really skeptical about is, if they both serve DHCP too. I imagine DDNS will not work flawlessly, though dynamic updates of Windows DNS from ISC DHCP seem possible.

Further reading:

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dns is not problem because is ip address witch is different. Is not good to run two dhcp server. You will not known witch server will response to dhcp request from client. Also you must prevent same ip address on one lan, but you can prevent this by spliting one net range. For example

win server

net range: xxx.xxx.xxx.1 - xxx.xxx.xxx.128
mask: 255.255.255.0
gateway: xxx.xxx.xxx.254
dns: xxx.xxx.xxx.yyy

ubuntu server

net range: xxx.xxx.xxx.129 - xxx.xxx.xxx.253
mask: 255.255.255.0
gateway: xxx.xxx.xxx.254
dns: xxx.xxx.xxx.zzz

This will avoid duplicated ip addresses.

Second solution is better but you must have switch-es. Create two vlan, split lan to two net ranges and put one dhcp server per vlan.

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