Global Catalogues

[mrforgetful]

So.

 

I'm looking into redundancy because at the moment as soon as server1 goes down noone can log on.

 

We have 5 identical spec servers.

 

server1 - DC, DNS, DHCP, GC and some peoples work

mailserver - Exchange, DNS and some peoples work

appserver - applications, Ghost, ALAN etc..

printserver - Print Server and some people work

 

I have just added the role of GC to printserver aswell, is this enough to provide redundancy?

I'm guessing not as if server1 goes I have nothing to provide DHCP.

Could I just add DHCP capability to printserver aswell?

Should I just add DHCP and GC and DNS to every server except appserver?

[tosca925]

I have DNS running on our second DC as well as the first. I have DHCP sitting on a second server that is in a standby mode (ready to be kicked in should the first DHCP server go down. It is set up with all the scope options and reservations. I export the DHCP scope nightly to a txt file and should i need to bring the second DHCP online i can quickly import the settings from the night before.

[ICTNUT]

@tosca925: How are you doing the DHCP export of an evening?

 

This is something i must get me head around but have not had the time to do so yet.

[GrumbleDook]

You only mentioned one DC. You need a second DC to allow people log on if the first fails, and that DC should also have DNS and GC.

 

If you have DHCP on it as well (80:20 rule) then it sort of balances everything out.

[Geoff]

@tosca925: How are you doing the DHCP export of an evening?

 

netsh dhcp dump >C:\dhcp.txt

[tosca925]

ICTNUT wrote:

@tosca925: How are you doing the DHCP export of an evening?

Code:

netsh dhcp dump >C:\dhcp.txt

 

I followed the MS article details below for a 2003 server.

Export the DHCP database from a server that is running Microsoft Windows Server 2003

To move a DHCP database and configuration from a server that is running Windows Server 2003 to another server that is running Windows Server 2003:

1. Log on to the source DHCP server by using an account that is a member of the local Administrators group.

2. Click Start, click Run, type cmd in the Open box, and then click OK.

3. Type netsh dhcp server export C:\dhcp.txt all, and then press ENTER.

 

Import

 

At the command prompt, type netsh dhcp server import c:\dhcpdatabase.txt all, and then press ENTER, where c:\dhcpdatabase.txt is the full path and file name of the database file that you copied to the server.

 

I put the follwoing netsh dhcp server export C:\dhcp.txt all into a CMD file on the DHCP server, then set a Schedule task to run at midnight nightly to back up to a network share on a different server.

 

Full MS article HERE

[Oops_my_bad]

We have 4 day leases on our IP's - if the shit hits the fan at least we'll have 4 days to rebuild the DHCP server :oops:

 

Wouldn't it be nice if you could load balance/failover DHCP without the 80/20!

[Kyle]

DHCP Clustering..................???

[sidewinder]

We have 4 day leases on our IP's - if the shit hits the fan at least we'll have 4 days to rebuild the DHCP server :oops:

 

Wouldn't it be nice if you could load balance/failover DHCP without the 80/20!

 

Remember though the machines would only keep their leases if they wernt switched off. On bootup they try and renew their lease, if they cant they end up with an 169.x address still

 

As for load balancing - I have DHCP on both of my DC's with the whole scope on both. On one I exclude half of the scope, on the other I exclude the other half. So each server issues roughly 50% of its addresses and the clients are roughly split 50/50 with what server they get their lease from.

And if one server was to go down, I would just remove the exclusion and let it do the whole scope

 

Ive got no idea whether thats a 'recommended' method but it works for us

Although it is pretty much like the 80/20 method - just with different percentages

[Geoff]

Remember though the machines would only keep their leases if they wernt switched off. On bootup they try and renew their lease, if they cant they end up with an 169.x address still

 

There's a microsoft specifc option you can set to instruct clients to release their lease on shutdown.

[mrforgetful]

You only mentioned one DC. You need a second DC to allow people log on if the first fails, and that DC should also have DNS and GC.

 

If you have DHCP on it as well (80:20 rule) then it sort of balances everything out.

 

Sorry they're all DCs.

 

After some reading yesterday I added DHCP to the printserver, now both DHCP servers have a superscope with all client machines scopes (we have one per main room and some per floor) within that. I've made the original DHCP server as it was serving between .100 and .200 and then on the new DHCP server I've added .50 to .99 in each scope.

They're both set to 4 day leases.

 

Seems to be working ok, just checked the newly configured server and it's leased an entire room )

 

Might try turning the main server off to see if it causes a problem...

[petectid]

We have 4 day leases on our IP's - if the shit hits the fan at least we'll have 4 days to rebuild the DHCP server :oops:

 

Wouldn't it be nice if you could load balance/failover DHCP without the 80/20!

 

This will only work if you never turn off your workstations, plus at about three days 75% of the lease period your workstations will attempt to renew their lease, if your server is down then they will fail.

[mrforgetful]

I know as we had it before if server1 went down then obviously nothing worked (as although we do have another DNS Server) it was the only GC and DHCP Server.

 

Now I've added the GC role and a bit more DHCP scope to another server (and set the scopes DHCP options primary DNS to the second DNS server), if my main server goes down clients should automatically use the remaining one?

[Geoff]

Er no, because windows takes a little while to notice the server has disappeared. It's usually quicker to reboot the machine than wait for it to figure out what is going on.

[mrforgetful]

Oh man!

 

So is it even possible to have it so that if one goes it's seemless?

 

Is that when I need to start using Clustering?

[Geoff]

Seamless? Don't be foolish. This is Windows.

[mrforgetful]

Seamless? Don't be foolish. This is Windows.

 

hehe, I forget sometimes and expect things to be perfect!

 

Well maybe I'll leave it all as is now and do some work people will actually notice...

[srochford]

I know as we had it before if server1 went down then obviously nothing worked (as although we do have another DNS Server) it was the only GC and DHCP Server.

 

Now I've added the GC role and a bit more DHCP scope to another server (and set the scopes DHCP options primary DNS to the second DNS server), if my main server goes down clients should automatically use the remaining one?

 

Yes - as long as your DNS is properly configured.

 

From startup you want 2 (or more!) DHCP servers - otherwise the machine can't get an IP and nothing much network will happen.

 

Once it's started it will query DNS for info about GCs and DCs - you need to have 2 DNS servers handed out by the DHCP so that if either goes you're still OK.

 

Provided that the DNS has the right info about GCs/DCs then as the machine starts up it will get an answer to query for DC etc that will let it you use either of the servers.

[Oops_my_bad]

As for load balancing - I have DHCP on both of my DC's with the whole scope on both. On one I exclude half of the scope, on the other I exclude the other half. So each server issues roughly 50% of its addresses and the clients are roughly split 50/50 with what server they get their lease from.

And if one server was to go down, I would just remove the exclusion and let it do the whole scope

How have you achieved this? And how do you set it up so that the 2 DHCP servers don't both try and lease an IP? Or is it just a case of the PC is leased the first one it gets?

[mrforgetful]

@srochford - cheers for clearing that for me. DNS should be set ok hopefully, both DHCP servers have two DNS addresses to use so think it will be ok.

 

@TeddyKGB - I'm guessing he's set both DHCP servers to use the same scope, you then set an exlusion range on both but one excludes the lower range and the other excludes the higher range. When one server breaks you just remove the exclusion that's set on the working server, there's a technet article on it but I don't have the link sorry.

On startup the PCs will send a DHCP query and the first server that gets it will handle the address.

[sidewinder]

Yeah thats exactly how I've done it