DHCP/VLAN question


We have the following network - PIX 506e--->Cisco 3550/2950 switches----> clients - all one VLAN (1).
We will shortly be upgrading the PIX OS to be able to handle two VLANs. VLAN2 will be for guests to use...we would like this to have access
to the internet only, therefore no inter-vlan routing.


The issue is how the clients in VLAN2 will pick up an IP address. I was thinking of creating a new scope on the DHCP server (which is in VLAN1) along with ip-helper address. Am I right in thinking -

i) If I create a scope on the DHCP server for VLAN2, it will automatically dish out addresses in the subnet because it knows that the request came form VLAN2? Likewise, it will continue to give out addresses for clients in VLAN1?
ii) The ip helper command does not enable intervlan routing, it simply allows the movement of DHCP messages between VLAN1's one and 2?

Or is it better to create a new DHCP server on VLAN2 so that there is no links between the two networks?

Would be grateful for thoughts from anyone that has implemented such a solution...

Thanks in advance.
Who is Participating?
pseudocyberConnect With a Mentor Commented:
IP helper would have to ROUTE the request onto Vlan1.  So, how are you going to do that without routing the vlans?

Perhaps the PIX could run a DHCP service for vlan2?
you have to create a new scope in the DHCP server for the other vlan and set in the switches your iphelper for the services dhcp and or bootp.
You could create the DHCP scope on the server like you suggested to begin with, using the helper address.  Then create an access list that only allows the gateway ( to route to the 192.168.1.x network.  Since dhcp is being retransmitted by the gateway, the access list will let that traffic through, but once the guest PC has an IP, it will no logner be able to route to the main VLAN.
I have to say your own thoughts are aright.
Dilan77Author Commented:
I think I'll go with the first suggestion, using the PIX as a DHCP server for that interface sounds best.

Thanks all for their input though.
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