How can I get DHCP ( layer 2 ) packets to forward between vlans on a network switch ?

Posted on 2007-10-01
Last Modified: 2008-01-09
We have 2 vlans and need to have the DHCP server on one vlan ( 500 ) and the dhcp clients on a different vlan ( 200 ).   Is there a way to forward the packets across the vlans ?   We want the vlan with the dhcp server to be isolated from the systems requesting the services except for DNCP and DNS.

Thank you all again.

Question by:itguy411
    LVL 23

    Expert Comment

    The only way to get vlans to communicate is with inter-vlan routing. you either need a layer 3 switch or a router to accomplish this.

    After setting that up you can create access list to filter the traffic you want
    LVL 10

    Expert Comment

    on a cisco switch there is a command you can type to forward DHCP requests to a DHCP server on a different VLAN.  the command is this.

    ip helper-address

    as that1guy said, this has to be done on the layer 3 device.  This particular command is entered in the VLAN config mode.
    LVL 10

    Accepted Solution

    if i remember, you are using dell switches, so refer to this page for some info on the Dell version of the helper-address command:
    LVL 33

    Expert Comment

    If its a Microsoft DHCP setup, you could always just use the  DHCP Relay service running on a Microsoft box to forward the packets, but this only works if the Vlans can route  to each other.  

    Author Comment


    Good suggestion and it is good to know, however in this case the microsoft server is in the other vlan thus would never see the packet to forward it.  
    LVL 10

    Expert Comment

    the helper command forwards all UDP broadcasts to the indicated address.  you need to configure this on your router that connects the two vlans.

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