DHCP Configuration in Nexus Switch

Anuoluwapo Fatokun · ‎07-22-2015

Hi all,

I need a help from you all, i just discovered that Nexus switches does not support dhcp server feature. I however plugged in a dhcp server on a access port say in vlan 10 on the interface vlans on the nexus switch configure dhcp relay to the dhcp server. I discovered only hosts in same vlan with the dhcp server picks ip addresses.

How do i make other vlans get ip address through the dhcp server.

thanks

Steve Fuller · ‎07-22-2015

Hi,

Assuming you have DHCP scopes enabled on the DHCP server for each of the VLANs, it sounds like you've not added the ip dhcp relay address command under the switch virtual interface (SVI) for the VLANs. The following should be sufficient:

!
feature dhcp
ip dhcp relay
!
interface vlan <vlan_number>
  ip dhcp relay address <dhcp_server_ip_address>
!

The ip dhcp relay address command within the interface vlan configuration is the command that will take the DHCP request broadcast from the client, and forward it via unicast to the DHCP server.

Regards

Anuoluwapo Fatokun · ‎07-22-2015

Thanks steve, i did configure all of that. My issue was hosts from other vlans apart from the vlan the dhcp server was connected to could not get ip address even though inter-vlan routing is working via hsrp.

Note is is vPC Topology domain

Steve Fuller · ‎07-24-2015

Hi,

Are you able to verify if the DHCP server receives a DHCP Discover from a client on one of the other VLANs, and then whether it sends the DHCP Offer?

If you're able then run the debug dhcp all command. That should show whether the switch is receiving the Discover, and what it's doing with it.

Additionally if you've packet capture capability on the DHCP server it would be useful if you could capture that and post here.

You might able to capture on the Nexus switch itself with ethanalyzer, but I've had mixed success with this tool. You could try ethanalyzer local interface inband capture-filter "udp port 67" (note that you need the double quotes) and check what that sees. You should at least see DHCP Discover being received from the client.

Regards