How to configure for handing out leases to identical subnets on seperate networks?
Simon Hobson
dhcp1 at thehobsons.co.uk
Wed Feb 3 21:40:50 UTC 2010
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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