Old Tired Question: 'Not configured to listen on any interfaces'

[Simon Hobson]

Alex Bligh wrote:

>>OK, I inferred that, but the fact that you have overlapping subnets also
>>means the network is broken - IP addresses are neither unique nor
>>globally routable.
>
>The whole point of RFC1918 is that multiple networks can use the
>same space. To be clear, customer A's numbering in 1918 space can
>intersect with customer B's, and the networks are not connected
>at all (they are virtual and isolated).

But still from an IP addressing POV, they break rules one and two. 
While they predate NAT, they were (I would expect) introduced for 
much the same reason - to allow larger networks without depleting the 
address space which it was realised a long time ago was not going to 
last forever.

>We have a virtual device which behaves like a dhcp server, but is
>actually relaying the packets. As far as the client is concerned, it
>is talking to a dhcp server.

So something else non-standard ;-) As an aside, why don't you have 
these devices get the address etc directly from the database and cut 
out the DHCP server which is suboptimal ?

>Given we are only doing fixed leases, renewals aren't important in
>our config, but I see no reason why such a config could not be
>adapted for dynamic leases.

You'd have a problem with overlapping subnets to the point where I 
doubt there'd be any advantage over a standard relay agent.



>The interesting point for me I can summarise thus: dhcp was originally
>designed such that
>1. The server ran on the same network as the clients
>2. The server would hold the canonical configuration
>
>In many use cases it would be better if neither of these assumptions
>need hold. However, ISC dhcpd, being designed a while ago, and
>being a reference implementation, tends to make this hard. Subnet
>0.0.0.0/0 is a useful hack, but probably only if you know what you
>are doing.

That's a fair summary - especially the very last bit.

-- 
Simon Hobson

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