IOS dhcp and multiple vlans

Unanswered Question
Oct 11th, 2007

hi all,

I have a router with multiple vlans that use the ip helper command. However, i need to define one particular vlan (for wireless option 43) for DHCP option 43. In the IOS of the router i can only define a global DHCP service. Here is my question - will the other vlans that request an IP address with they get the IP address defined on the global IOS defination or continue to use the IP helper IP address?

I have this problem too.
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lgijssel Thu, 10/11/2007 - 09:34

An ip helper forwards the dhcp requests to a dhcp server elsewhere on the network.

Each subnet (=vlan) has a scope there.

Option 43 should be configured only on the scope(s) where you want this option to be added in the response.

Note: You are incorrect in the assumption of certain limitations on the IOS-based dhcp server. You can add multiple dhcp scopes on a router and each scope can have different options.



nathancielieska Thu, 10/11/2007 - 11:15

If an ip helper-address is configured on the interface which receives the DHCPDISCOVER packet, the packet will be converted to a unicast packet and sent to your DHCP server configured in the helper address.

If a packet is received on an interface not configured with a helper-address, the router DHCP will process it.


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