My Lan is working fine 5 switches connected to core switch and have a router, DHCP configured in the router, network, -- Mask -- d.g (Router IP).DNS ETC,

we want scenario to be like this: Clients use DHCP in new DHCP server but when server is down sure they can be online with router DHCP

NOW we have one server configured as AD,DNS and DHCP server, sever have ip DNS no default G.t

when i configure DHCP server give it router ip as a router D.G ( ) and also server ip in DNS (primary Server ip and DNs of google)

now not all my PCs have IP from DHCP server,

SO clint use Server DHCP have somthing like that:

ip : 10.10.10.x




and of course i can join them to AD

Clients use Router DHCP have :

ip : 10.10.10.x




so of course can't join AD.

i need them to get their ips from server without remove dhcp server in router as an alternative DHCP what i can do in server or router.

  • what is the right Ips assigned in DHCP server and DNS.
  • what i will add in router (DNS of my server) or refer to DHCP sever or donothing on it?

  • what clients D.g should be in this case the ip of router or the ip of the server.


I just need 2 simple things

1- clients get ips from DHCP SERVER and can joined AD in the same server

2- Clients can access internet through router

NOte:(Router and server in the same core switch and confiured DHCP in both of them with the same range) what is the best implementation for that?

  • in the future we will have another server as aTMG server sowhat i give to clients as D.g : - ip of (AD,DNS,DHCP server) and give it the d.g of TMG or give clients D.g ((tmg ip directly)) Oct 9 '15 at 12:33
  • 3
    Don't do this. If you have AD and if the clients are joined to the AD domain then they should ONLY use the AD DNS server for DNS. If you have a problem with keeping the server up then you should fix that instead of designing some cumbersome workaround that's likely going to make things worse, not better.
    – joeqwerty
    Oct 9 '15 at 15:17
  • what about Now with one server, what is the right ips and DNSs should i give to server in DHCP Configuration to do just 2 things: 1- can join users to AD (ad is the same DHCP server with ip 2- Users can access internet through router ( Oct 9 '15 at 16:19

Don't try to do DHCP failover depending on whether a server is up or down. It won't work very well, if you can get it to work at all.

What might work in your scenario, and would be resonably clean, is that you run DHCP in the router, and configure the router's DNS server to forward requests for your domain back to your domain controllers. Few router softwares will do this however. pfSense will do it through the DNS Forwarder functionality, but most others can't. We can't really give you specific advice since you don't say what router is in use.

However, a much better idea is just spending a few hundred dollars on a second server to act as your second domain controller. You might then run DHCP in a failover configuration on these two servers. You would assign two DNS servers through DHCP pointing at your two domain controllers.

  • my router is cisco 1921 Oct 10 '15 at 21:26
  • Nice answer bumped to the homepage by Community. DHCP failover is tricky even with two domain controllers, as it would require a common place to save the lease data, which would still be a single point of failure. Sep 15 '19 at 6:21

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