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New Member

Vlans and DHCP

My new LAN wil have 37 Catalyst switches (02 Cat 6505, the backbone).

I am considering to create 04 vlans. Questions :

Should each VLAN use different subnetworks ?

Which Vlan my DHCP server must be placed into ?

How does the DHCP server know what IP address to assign according to the vlan? I mean, if a PC in vlan 1 sends a broadcast, DHCP server must give it , let´s say, , if PC belongs to vlan 2, gives, and so on.... is it a router config issue or DHCP one ? How ?

Should server farm have a different subnet and vlan than the one for PC clients ?

I appreciate all your comments and help...


Cisco Employee

Re: Vlans and DHCP

Yes, you need each VLAN in a different subnet. The DHCP server can be in any VLAN. Just set up multiple scopes for all the VLANs you have and use the helper addresses on VLAN interfaces to forward the DHCP broadcast across VLANs. Regarding server farm being in a different subnet, it's not a neccessity but more of a design issue

New Member

Re: Vlans and DHCP

Thanks for your help. I have created interface vlan 1, 2 & 3 in some switches, using helped addresses,but vlans 2 & 3 are shutdown; when I do "no shutdown" and then show runn... interfaces are still shutdown....

what´s the problem ?

any good link for vlans.. ?

Cisco Employee

Re: Vlans and DHCP

You need to have some devices in the layer 2 VLAN for VLAN interfaces to be up. This is due to autostate behavior. Assign some ports to vlan 2/3, connect some devices

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