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2 DHCP Server

Posted on 2002-05-14
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Last Modified: 2013-12-19
Can we have 2 DHCP Server in different segment? or it have to in same segment?

Thanks in advance
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Question by:plusign3
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by:escheider
ID: 7010037
Yes and Yes.

Yes, multiple DHCP servers can exists in multiple segments or in the same subnet.

Multiple DHCP servers in the same subnet should service different ranges in the same subnet.  This is commonly used for redundancy in case one DHCP server were to go down.

What are your plans with the two DHCP servers?
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Expert Comment

by:TooKoolKris
ID: 7011211
You would 2 in the same segment as a means of redundancy. You would create split scopes.

You can implement split scopes, create identical scopes, and exclude opposite portions of the address range on each DHCP server. For example, assume that there are two DHCP servers: DHCPServerA and DHCPServerB. Both servers serve the 192.168.1.0 subnet, where the host addresses is between 192.168.1.1 and 192.168.1.254. In this example, the scope is split in half.

On DHCPServerA, create a scope with a start address of 192.168.1.1 and an end address of 192.168.1.254, and then create an exclusion from 192.168.1.127 to 192.168.1.254.

On DHCPServerB create the same scope: the start address 192.168.1.1 and the end address 192.168.1.254. Then, create an exclusion from 192.168.1.1 to 192.168.1.126.

A scope can also be divided between more than two servers in a similar way using the preceding guidelines.

If you create two Microsoft (MS) DHCP servers with the same scope without any exclusions, you can cause each DHCP server to send a NACK request from the opposite DHCP server. This configuration may result in clients that are unable to obtain leases, or clients that take very long periods of time to obtain leases.

You can confirm this behavior by examining Event Viewer for event 1011. Also, the DHCP Audit log lists any corresponding DHCPNACK entries.

If the 2 different segments are split with a router then you should use a DHCP sever on each segment because unless you configure relays DHCP wont forward across a router.

Hope this helps,

TooKoolKris
MCSE+I, CCNA, A+
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Author Comment

by:plusign3
ID: 7011581
I am planning to provide redudancy, in case another segment/switch is down.

Is there any documentation/links to tell how router can handle 2 MS DHCP in different segment?

We are using Cisco router/switch.

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TooKoolKris earned 100 total points
ID: 7011750
You can have 2 DHCP severs in different segments with no problems as long as each server is only leasing addresses to the segment that it is on. If you need the server to be able to lease addresses to different segments other then the ones to which they belong and a ROUTER (not a switch or hub) is between the segments then you need to read below.

If you are planning to have clients obtain an IP lease from a DHCP server in another segment that crosses a router you will need to do the following.

1.)Configure a BOOTP/DHCP Relay Agent on the client segment. This can be the router itself or a Windows NT computer running the DHCP relay service.

2.)Configure a DHCP scope to match the network address on the other side of the router where the clients are. Make sure the subnet mask is correct. - Do not configure a default gateway on the DHCP server's NIC such that it is the same address as that of the router supporting the subnet where the clients are. - Do not include that subnet's scope in any superscope that is configured on the DHCP server's LAN segment.

"How to Configure Microsoft DHCP Server for BOOTP Clients (Q174765)"

http://support.microsoft.com/default.aspx?scid=kb;en-us;Q174765

TooKoolKris
MCSE+I, CCNA, A+
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Author Comment

by:plusign3
ID: 7014197
Do you have from Cisco? or how network should be configured?

The reason i ask this because my vendor said it can't be done.

Thanks again

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Expert Comment

by:TooKoolKris
ID: 7014514
If the vendor isn't smart enough to figure this out then I would take a close look at your vendor. Most people use the word "can't" instead of "I don't know how". If you setup up the DHCP relay on the Server you wont have to do anything to the router. The relay will make sure that the request get forwarded to the other segment.

TooKoolKris
MCSE+I, CCNA, A+
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Expert Comment

by:andyalder
ID: 7015846
On Cisco you use ip helper instead of bootp relay:

ip helper-address 10.1.10.10
ip helper-address 10.1.10.11

which forwards broadcasts from the local subnet to these two IP addresses, see the diagram at the bottom of http://www.cisco.com/warp/public/779/smbiz/service/knowledge/tcpip/dhcp.htm
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Author Comment

by:plusign3
ID: 7071908
andyalder,
You should get the point too, but i don't how give point for 2nd person.

TooKoolKris has explained very details and the point will go to him too.
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