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Dhcp issue

Hello,

I have 2 4500 core switches and access switches.I also have 10 vlans.How can i enable dhcp on the core switch so that it assigns ip address to each vlan ?(each vlan has a different class C address space)

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Dhcp issue

If a port belonging to vlan 2 initiates dhcp request on the access switch how can the core switch know the address space of the host connected to the port belongs to?

You'll have your hosts assigned by port to vlan 2, and the port that connects to the core will have a trunk that allows vlan 2 over the trunk. The switch will see vlan 2 tagged in the frame and will assign based off of that. The switch is smart enough to know that the dhcp pool you created and the network that's under that will be supported under that particular vlan based off of the ip address that's assigned to your SVI.

HTH, John *** Please rate all useful posts ***
5 REPLIES

Re: Dhcp issue

You would set up a helper address under the vlan's svi, and then point it to a dhcp server that has all of the scopes that you want to support.

vlan 1: 192.168.1.0/24

vlan 2: 192.168.2.0/24

vlan 3: 192.168.3.0/24

DHCP server's address: 192.168.1.50

DHCP server's scopes:

192.168.1.0/24

192.168.2.0/24

192.168.3.0/24

int vlan 1:

ip address 192.168.1.1 255.255.255.0

int vlan 2:

ip address 192.168.2.1 255.255.255.0

ip helper-address 192.168.1.50

int vlan 3:

ip address 192.168.3.1 255.255.255.0

ip helper-address 192.168.1.50

I'm assuming that you have ip routing enabled on the switch, so the above should be all that you would need to do. In your scopes, you would set the default gateway as the respective SVI.

HTH,

John

HTH, John *** Please rate all useful posts ***
Community Member

Re: Dhcp issue

Your solution assume that dhcp is implemented on a server but i want it to be implemented on the core switch because windows can not accomodate 20 scopes of 254 addresses each.

Re: Dhcp issue

Same concept then, except remove the helper addresses and create your scopes on the switch:

ip dhcp pool VLAN1

network 192.168.1.0

default-router 192.168.1.1

domain-name test.com

dns-server

ip dhcp pool VLAN2

network 192.168.2.0

default-router 192.168.2.1

domain-name test.com

dns-server

etc...

HTH, John *** Please rate all useful posts ***
Community Member

Re: Dhcp issue

How can the core switch maps ip addresses to the respective vlan ?

EG: If a port belonging to vlan 2 initiates dhcp request on the access switch how can the core switch know the address space of the host connected to the port belongs to ?

Re: Dhcp issue

If a port belonging to vlan 2 initiates dhcp request on the access switch how can the core switch know the address space of the host connected to the port belongs to?

You'll have your hosts assigned by port to vlan 2, and the port that connects to the core will have a trunk that allows vlan 2 over the trunk. The switch will see vlan 2 tagged in the frame and will assign based off of that. The switch is smart enough to know that the dhcp pool you created and the network that's under that will be supported under that particular vlan based off of the ip address that's assigned to your SVI.

HTH, John *** Please rate all useful posts ***
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