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DHCP/VLAN question

Posted on 2006-10-26
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Last Modified: 2010-03-19
Hi

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.

VLAN1: 192.168.1.0/24
VLAN2: 192.168.2.0/24

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 192.168.2.0/24 subnet because it knows that the request came form VLAN2? Likewise, it will continue to give out 192.168.1.0/24 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.
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Question by:Dilan77
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5 Comments
 
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pseudocyber earned 750 total points
ID: 17812984
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?
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by:mahe2000
ID: 17813480
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.
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Expert Comment

by:Sean64
ID: 17813771
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 (192.168.2.1) 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.
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Expert Comment

by:igmp
ID: 17818723
I have to say your own thoughts are aright.
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Author Comment

by:Dilan77
ID: 17842920
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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