Using two DHCP servers on LAN

Posted on 2010-11-29
Medium Priority
Last Modified: 2012-05-10

I am using a broadband wireless as my backup internet connection, my primary is using ADSL with a PIX 506 firewall.  My ISP recommend me to use Ericsson W30 or W35 broadband router for the WIFI internet, and this Ericsson W30 or W35 come with DHCP server feature.  I am currently using my Windows DC as DHCP server, therefore all LAN user get the IPs from this Windows DHCP server.

Because the Ericsson W30 or W35 will be used as a wireless internet access point and the backup internet, I have to turn on the DHCP server function on this router in order to support wireless users but the problem is that if I turned it on; there might be some conflict for the LAN users.  So what can I do?

My current ip structure is that

ip : -
subnet mask :
Gateway :      (primary internet connection)

The ip on Ericsson W30 router will be for backup internet and normal wireless.

In this case; if someone uses Wireless; he / she always access to internet through Ericsson router which is

The gateway and gateway will be attached to LAN 24x7.

Because both gateway is on 24x7, if I turned on the DHCP server on gateway, I afraid that the normal LAN user will be the ip from this DHCP server and going to internet from gateway too.  I just want to the LAN user uses gateway if the primary internet connection failed ONLY.

Any idea?

Question by:KANEWONG
1 Comment

Accepted Solution

Grant Berezan earned 1000 total points
ID: 34232643
Two options come to mind:
If you need the wireless users to access your network, you should disable the DHCP on the WAP/router and let the DHCP be assigned by the Windows server exclusively.
If you want the Wireless users NOT to have access to your network, you will need to put the Ericsson on a VLAN or the like.
Only one DHCP server can ever be on a single VLAN, and the WAP will normally pass through DHCP to any wireless clients that successfully authenticate.

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