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

Glenn Satchell glenn.satchell at uniq.com.au
Sat Feb 26 00:12:55 UTC 2011

On 02/26/11 04:24, Matthew Causey wrote:
> Hash: SHA1
> Thanks for the insight guys.  This is very helpful (even the slightly
> off-topic sub thread. :-)
> On 2/24/11 1:24 PM, Glenn Satchell wrote:
>> On 02/25/11 05:49, Simon Hobson wrote:
>>> Matt Causey wrote:
> <snip>
>>>> What I did as a workaround was created a /32 subnet declaration for
>>>> the ip address on eth0 so dhcpd would run.
>> You should use the proper subnet for this definition. It helps dhcpd
>> build an internal picture of the network structure. Something like this:
>> subnet a.b.c.0 netmask a.b.c.d { }
> What are the potential negative side effects of using:
> subnet netmask { } (local server ip/32)
> vs
> subnet netmask { } (the /22 where server lives)
> - --
> Matt

One item I haven't seen mentioned in this fascinating discussion is to 
do with scoping.

If you define the subnet(s) to represent the actual network layout then 
you can define things such as 'option routers', dns servers, various 
class things, and so on, in the right scope and the values will be 
inherited by all the things that fit in that scope. This can simplify 
and add flexibility to the config.

In the original question the dhcp conf effectively defined a host 
statement that contained ip address, subnet mask, broadcast, default 
router, dns servers, etc, etc. If a client moves to a different subnet 
then all of this becomes invalid and needs to be changed. However, if 
using scoping to provide the extras, then changing the IP address puts 
the client in a different scope and inherits the values that are 
appropriate for that scope.

I'm not sure this makes that much difference with a DB backend or a 
script that generated dhcpd.conf, but it is worth noting IMHO.

One other thing regarding fixed addresses versus dynamic allocation. 
None of this matters to the client. The client still makes the same 
requests, acks, etc, in all cases. It just happens that the server 
always hands back the same address. Handing back a fixed address is 
purely an internal server function.

Glenn Satchell                            |  Miss 9: What do you
Uniq Advances Pty Ltd, Sydney Australia   |  do at work Dad?
mailto:glenn.satchell at uniq.com.au         |  Miss 6: He just
http://www.uniq.com.au tel:0409-458-580   |  types random stuff.

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