Solved: how PC assign IP address from DHCP from another VLAN ?

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Muhammed-Rummaneh🇸🇾

how PC assign IP address from DHCP from another VLAN ?

Dear Experts :
I need to ask a question about VLANs and DHCP ( IP assignment )

Case:
I have 4 Cisco Switches and already configured with VLANs as follow:
- Core Switch (VLAN2 , VLAN3 , VLAN4 )
- 3 Floor switches ( VLAN 2, VLAN3 , VLAN4 )
- Server ( DNS , DHCP , DC )
As you see in the diagram DHCP server IP address : 192.168.1.100
All I need : how PC from another VLAN ( IP subnet 172.16.1.X ) can assign IP address from DHCP

Please Explain this case to me in details
Thanks

DHCP.jpg

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bbao🇦🇺

basically, you need to enable DHCP Relay on the core switch if it also does L3 routing.

additionally, you need to configure the central DHCP server for the subnets of other VLANs.

hope it helps,
bbao

GJHopkins🇦🇫

On the interface which is the default gateway for each VLAN you need to add

interface vlan xx
ip helper-address 192.168.100

and setup scopes on the server.

Rick_O_Shay🇺🇸

What happens is the client PC's that are looking for an IP address assignment via DHCP send out broadcast requests to any DHCP server that might be listening. The broadcast won't go across a VLAN/subnet boundary so the Layer 3 switch or router’s interface for that network needs to be set up to relay that DHCP request via a unicast packet to the DHCP server on whatever subnet it is attached to. This is done with the IP Helper or DHCP relay configuration on each of the router’s IP interfaces.

The server needs to have a scope built for the other subnets and when it gets a request relayed by a router it knows what subnet it came from based on the relay agent address the router puts in the packet. The server then replies with an address from the correct pool of address for that subnet and sends it back through the router to the client.

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GJHopkins🇦🇫

Yes and my commands should read

interface vlan xx
ip helper-address 192.168.1.100

the IP address of your server of course

Muhammed-Rummaneh🇸🇾

ASKER

thanks of all

can any one advice me in detail and give me example from internet ( same case )

thansk

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GJHopkins🇦🇫

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GJHopkins🇦🇫

If you don't have VLAN interfaces on the 4510 you will need to set them up, you can only route between the VLANs if a router has interfaces in both VLANs.

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Muhammed-Rummaneh🇸🇾

ASKER

Thanks

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A router is a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. The most familiar type of routers are home and small office cable or DSL routers that simply pass data, such as web pages, email, IM, and videos between computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.