How to configure for handing out leases to identical subnets on seperate networks?

[Simon Hobson]

Antonio Goméz Soto wrote:

>I want dhcpd to manage leases for a lot of SOHO networks where dhcp-relay
>is configured. But some locations might want to use the same ip ranges.
>
>For example there might be different remote networks all using 192.168.0.0/24
>
>Can this be done?

Not with any standard DHCP package. The first 
problem is that the IP addressing is ambiguous 
(one of the two reasons that NAT == fundamentally 
broken).

The second problem is that clients don't use a 
relay agent to renew existing leases, they 
unicast to the DHCP server, and the DHCP server 
unicasts the reply (unicast = send a packet 
directly addressed to a remote device by it's IP 
address). This is the second problem that NAT 
introduces - you no longer have end to end 
routability since the RFC1918 addresses aren't 
accessible from outside the NAT (the second of 
the two reasons NAT == fundamentally broken).

To handle leases for devices behind the NAT 
gateways, you will have to configure a means of 
routing traffic between those networks and the 
DHCP server which does NOT go through NAT. For 
many SOHO gateways this isn't possible, and for 
those where it is, the management issues are 
non-trivial (such as managing lots of VPNs).

-- 
Simon Hobson

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