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New Member

multiple DHCP Subnet through V lan

Dear All,

i like to request a help, i am not good in cisco anyone can explain me  it will help for me.

i am trying to configure muliple dhcp subent through Valn

1. i create a dhcp server and create 3 subetnet

a. my network card ip dhcp enabled

b . configure DHCP scope for and

2. i have sonicwall firewall with router there i create 2 valn .

3. cisco switch sg300-28p also create valn. ( valn 20 port 3-5) (Vlan 30 port 7-10) create a trunk port for both Vlan port number 2.

i give conection from sonicwall to switch trunk port 2 and connect laptop to valn 20 port i am getting range ip, if i connect to laptop to Vlan 30 also getting Vlan 30 range IP.( this time Sonicwall DHCP is enabled)

now come to the point, i need to relase DHCP from my server, so i disable dhcp from Sonicwall. and enable dhcp from server.

but i am not getting ip address from server to any valn.

i create a trunk port for DHCP server and connect to there. then also same problem

please help to configure the best way.


multiple DHCP Subnet through V lan

Hi Bino, I'm guessing the Sonicwall supported the VLAN tags and internal routing required to make the DHCP work. Your DHCP server may be missing option 82 or it may be missing routes to get the DHCP message across the VLANs.

Please mark answered for helpful posts

-Tom Please mark answered for helpful posts
New Member

multiple DHCP Subnet through V lan

what you have to do is configure ip helper addresses on your vlans to point to the new server, it was probably pointing to your sonicwall which is why it was working on the sonicwall, but once you changed over to your server, you have to convert it over to your new dhcp server.

without port forwarding your switches/routers do not know where to send those requests, especially if they are on different vlans.  thats one ceveat to running vlans and switches, it doesnt like flooding out requests to every port.

it appears to be under:

ip config - udp relay/ip helper

that section, add your new dhcp server to that and it should fix it so it sends your dhcp requests to your dhcp server.


multiple DHCP Subnet through V lan

The IP helper for DHCP is unavailable because there is a dhcp relay configuration which also supports option 82.

Please mark answered for helpful posts

-Tom Please mark answered for helpful posts
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