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Re: 4800g vlan and DHCP server

Occasional Visitor

4800g vlan and DHCP server

Ok history first I have a current network

with 2 older 4880 switches with a Vlan

Switch one is the core switch 192.168.160.X core 2 has a vlan 192.168.161.x

The Dhcp server is on a windows 2008 machine

I used the udp helper on the vlan switch and the vlan Pcs get there ip numbers from the dhcp server on the windows machine.


We are replaceing the current switchs with new 4800G with 10 gig connection


So I need to set up the new 4800G swatches and I find that the gui is missing

many many features most importantly the udp helper.:smileysad:


I can't figure out how to get the 192.168.161.X vlan  network to get to the dhcp server

Frequent Advisor

Re: 4800g vlan and DHCP server


Download this manual.

Chapter 12 UDP Helper Configuration.



Occasional Visitor

Re: 4800g vlan and DHCP server

i will look but the book for the 4800g says that the udp helper  does not do the ports for dhcp servers

Frequent Advisor

Re: 4800g vlan and DHCP server

Suppose that the win2008 dhcp server is in the net 192.168.160.X and its ip address is THEN:



dhcp enable

dhcp relay server-group 1 ip

interface vlan-interface 160

dhcp select relay

dhcp relay server-select 1


That is it!

Occasional Advisor

Re: 4800g vlan and DHCP server

Mr. krbaugh, how are you?


I am having some problems with DHCP and a switch 3com 4800g, the difference is

my DHCP server is still a Win 2003 Server and not a 2008 like yours.

Can you share some insight as to how your infrastructure is set up?


I attached an image of what I am trying to set up. I have configured the IPs of the interfaces,

the default route and the relay on port 2. I have also set port 2 as trunk in order to have all traffic

from all other vlans go through it.

I am able to ping each individual interface with a host in the same network. Except the trunk interface.

I cannot reach any other interface but the one I am connected to and as a result I cannot get an IP address

from the AD. Anything you can share would be helpful.






Trusted Contributor

Re: 4800g vlan and DHCP server

Port 2 shouldn't be a trunk, and the DHCP "ip helper" needs to be on the routing interface for the subnet the request is coming from - ie, the supplicant's default gateway.