Separates VLANs with the same IP-Range

Simon Hobson dhcp1 at
Sat Apr 27 16:02:01 UTC 2019

german181 at wrote:

> So i remove the nat konstrukt and add a subnet for the second relay.

It's not entirely clear what your network topology is here. Are you saying that there is NAT between the DHCP server and the clients ?

There must be no NAT between clients and server - the server needs to be able to send unicast packets to the client and this cannot be done if there is NAT in the path.
Also, you cannot have any overlap in IP addressing between networks - normal packet routing doesn't handle this, and the ISC DHCP server certainly doesn't.

Remember two two fundamental rules of IP are "addresses must be globally unique"(1) and "any node should be able to address a packet to any other node"(2). NAT breaks both of these.

1 - In the context here, in the collection of networks your DHCP server is to handle, all addresses must be unique.

2 - Obviously these days subject to administrative restrictions (ie firewall filters). But again for your context, the DHCP server and any client it is to support must be able to address unicast packets to each other and have them delivered.

More information about the dhcp-users mailing list