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Cisco Swtich dhcp ip-helper address command

Last night I changed the IP address of my dhcp server which resides on a Windows server.  I forgot to change the ip-helper entry for the vlan interfaces on our switch, so that broke dhcp.  This morning I went in and removed the old ip-helper address entry and entered the new one.  I thought that would take care of it but the requests aren't getting through.  I can see by my dhcp logs that the dhcp server is not getting the requests.  Is there something I have to do to clear/refresh so that the new ip-helper address entry works?
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jpletcher1
Asked:
jpletcher1
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1 Solution
 
bsohn417Commented:
int vl xx
ip helper-address 172.16.x.x

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bsohn417Commented:
u also have to remove old address by

int vlxx
no  ip helper-address 172.16.10.10
ip ip helper-address 172.16.x.x
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jpletcher1Author Commented:
Yes, this is what I did this morning.  I removed the old entry and added the new entry to the vlan interface, but it still doesn't seem to be working.  
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rochey2009Commented:
Hi,

From the PC, have you tried forcing a release then renew

ipconfig/release

ipconfig/renew
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jpletcher1Author Commented:
Yes, I have tried that many times and then also rebooted them.
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jpletcher1Author Commented:
This issue seems to be this...  The new IP that I gave the dhcp server is on a different subnet/vlan than the clients.  Before the clients were on the same subnet/vlan.  I thought the ip-helper command was supposed to bascially relay all dhcp requests to the specified dhcp server, even if it is on a different subnet.  Am I missing something?
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rochey2009Commented:
can you ping the default gateway of the LAN where the PC's are located from the dhcp server?

Do you use DHCP snooping on your switches?
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jpletcher1Author Commented:
I figured it out.  The vlan interface had a primary and secondary IP address on it.  The DHCP scope was setup for the subnet that the secondary IP was on.  I'm guessing that the ip-helper address goes by the primary IP address only and not the secondary.  I'll reverse the order of the primary and secondary IP for the interface and then it will be fine.
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rochey2009Commented:
That's correct, ip helper only works with the primary address.
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