using dhcp through vlans

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May 2nd, 2007
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Hi all, If my dhcp server address sits on vlan 1 subnet at the moment giving out ip addresses for that vlan, If I add another scope on there for another vlan im creating, will these addresses be also dished out on vlan 1, I know I use the ip helper address command, without this what will happen ?



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mohammedmahmoud Wed, 05/02/2007 - 23:18
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Hi Carl,

DHCP uses broadcasts accordingly it can never be interoperable between 2 VLANs without inter VLAN routing and IP Helper.

But the problem is that the new scope will also be used in the same VLAN 1.

HTH, please rate if it does help,

Mohammed Mahmoud.

carl_townshend Thu, 05/03/2007 - 02:08
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so how would I get around this? when I configure ip helper on my switch, will it stop the scope being offered out via vlan 1 ?

mohammedmahmoud Thu, 05/03/2007 - 02:25
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Hi Carl,

Only one way to go around, is to have 2 NICs on the DHCP server each NIC shall be in a different VLAN (one for VLAN1 and the other for VLAN2), with 2 scopes configured (one in the first subnet and the other in the second subnet),when the hosts in VLAN1 broadcasts to the DHCP interface on thier subnet it will lease them an ip from the scope with the local subnet, and vice versa for VLAN2 and you won't be needing ip-helper.

HTH, please do rate if it does help,

Mohammed Mahmoud.


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