I am confused: IP address for different hosts in different VLANs

halaakajanhalaakajan Member Posts: 167
in CCNA & CCENT
I am confused.

How does an IP address is given from a Microsoft DHCP server to the clients. Lets say we have around 6 scopes (Computer,Wireless,Printers,etc) in the DHCP server. How does the server know which range to give the client ip address from? Is it because of the "ip helper address" command in the Cisco switch?

Please explain.

Your help will be very much appreciated.
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Comments

  • RouteMyPacketRouteMyPacket Member Posts: 1,104
    We can assign IP Helper on each VLAN interface

    Example:

    Interface VLAN 1
    192.168.1.1 255.255.255.0
    ip helper-address 192.168.10.254

    Interface VLAN 2
    192.168.2.1 255.255.255.0
    ip helper-address 192.168.10.254


    and so on

    So each time a DHCP broadcast goes out, it will hit it's DG right? Ok now that we have the ip helpewr address applied it will pass it along to the scope that matches the vlan subnet
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  • f0rgiv3nf0rgiv3n Member Posts: 598 ■■■■□□□□□□
    To add to that, the server knows which range to give it because of the interface IP of the VLAN. So when it comes from vlan 20 which has an ip of 192.168.¿.1, the server will notice in the packet that the request is coming from 192.168.¿.1 and grab IPs from that range. Also, sometimes you need to give the DHCP server additional information in order to have it react in certain ways, look up option 82.
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  • ZartanasaurusZartanasaurus Member Posts: 2,008 ■■■■■■■■■□
    There is a field in the DHCP packet called GIADDR (gateway address). Devices that are performing DHCP relay stamp their IP from the interface they received the DHCP discover message from. The DHCP server looks at the GIADDR and offers an IP from that range.
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  • fadhilfadhil Member Posts: 200
    there is some devices like printer,server and other devices in which their ip address are not change are configured statically(for a special device like printer or a gateway) so dhcp server knows a certain ip address should given a host or client so other ip addresses may be given other clients.
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  • emerald_octaneemerald_octane Member Posts: 613
    The above info is good. Seriously configuring vlan/subnet dhcp on win server is so easy your head will spin. It just works.
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  • 2URGSE2URGSE Member Posts: 220 ■■■□□□□□□□
    halaakajan wrote: »
    Is it because of the "ip helper address" command in the Cisco switch?

    This command forwards UDP broadcasts (DHCP) across an interface.
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