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Cisco ip helper address doesn't work for DHCP Packets

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Last Modified: 2015-08-03
Hi Guys,
I have a Cisco 3750 Stack.
My goal is to change the IP range for Vlan1.

OLD IP RANGE: 172.27.187.0/24  (current)
NEW IP RANGE: 10.10.70.0/24 (new IP range)

I just configured the following

interface Vlan1
 ip address 10.10.70.1 255.255.255.0 secondary
 ip address 172.27.187.254 255.255.255.0
 ip helper-address 10.10.88.100
!

I have a new DHCP Server in the server 10.10.88.100 (Vlan88) giving out IP addresses in the 10.10.70.0/24 IP range that works, I have tested it with  a test vlan and connected a test computer to the test port and the ip helper worked on that test.

Now I disabled the current DHCP Server in Vlan1 (production environment) that is giving out IP addresses in the range (172.27.187.0/24) and added the ip helper line as shown in the configuration above.

But this time it didn't work, meaning that none of the computers in vlan1 were able to see the DHCP Server.

Now that I'm writing this I'm thinking that it could be that the 10.10.70.1 is a secondary IP address in Vlan1, may be it needs to be the primary IP address of that Vlan1 so that the DHCP Server identifies that the computers in Vlan1 can receive IPs in the 10.10.70.0/24 range. But all this are just ideas.

Can somebody please shed some light on this issue?

Thanks.
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