How does DHCPD determine what IP address to assign and...

[Ryan McCain]

Sorry to spam the list but I made a typo.  The 

  option routers 10.116.6.1;

should be 

  option routers 10.116.6.254;

Sorry for the confusion.


>>> On Fri, Dec 21, 2007 at  3:07 PM, in message
<476BD6BB.5D1A.003A.0 at dss.state.la.us>, "Ryan McCain"
<Ryan.McCain at dss.state.la.us> wrote: 
> I might have figured it out.  Unfortunately there is no one here to test due 
> to the holidays:
> 
> class "DialUp" {
>     match if substring(option vendor-class-identifier, 0, 9) = "ASYNC";
>         log (info, " Matched Dialup Rule");
> }
> 
> subnet 10.116.6.0 netmask 255.255.255.0 {
>     pool {
>         allow members of "DialUp";
>         range 10.116.6.1 10.116.6.8;
>         option routers 10.116.6.1;
>         }
> }
> 
> <SNIP>
> 
> #VPN
> subnet 10.116.6.0 netmask 255.255.255.0 {
>   range 10.116.6.9 10.116.6.179 ;
>   option routers 10.116.6.1;
> 
> ...
> 
> ..Will this reserve IP addresses 10.116.6.1 - 10.116.6.8 for DHCP clients 
> with a UID that contains ASYNC?
> 
> 
> 
> 
> 
> 
> 
>>>> On Fri, Dec 21, 2007 at  2:46 PM, in message
> <476BD1DB.5D1A.003A.0 at dss.state.la.us>, "Ryan McCain"
> <Ryan.McCain at dss.state.la.us> wrote: 
>> I found a few posts in the archives but am a bit confused.  I don't know 
> what 
>> the 0 and 9 are for and used the example I found as a template.  I am on the 
> 
>> right track if I want all DHCP clients that connect w/ the UID containing 
>> ASYNC be assigned IP addresses between 10.120.5.100-108 only??
>> 
>> 
>> class "DialUp" {
>>     match if substring(option vendor-class-identifier, 0, 9) = "ASYNC";
>>         log (info, " Matched Dialup Rule");
>>         range 10.120.5.100 10.120.5.108
>> }
>> 
>> ..Thanks..
>> 
>>>>> On Fri, Dec 21, 2007 at 12:40 PM, in message
>> <a06240822c391b86b364d at simon.thehobsons.co.uk>, Simon Hobson
>> <dhcp1 at thehobsons.co.uk> wrote: 
>>> Ryan McCain wrote:
>>> 
>>>>1) If I have a defined scope of 10.120.5.1 - 10.120.5.180, whill 
>>>>DHCPD hand out .1 to the first DHCPD client, .2 to the second and so 
>>>>on?  Or is there another algorithm thats used?
>>> 
>>> No, officially the initial order is undefined - in practice, the 
>>> current implementation will allocate unused leases from the highest 
>>> address down for no other reason than the way they are hashed 
>>> internally.
>>> 
>>> Once there are no "never used before" addresses left, addresses are 
>>> recovered from expired leases on a least recently used basis.
>>> 
>>>>2) Is it possible to assign a subset of IP addresses in my scope to 
>>>>DHCP clients whos UID identifier contains a specific string?  For 
>>>>example, all dialup users have ASYNC in their UID.  We'd like to be 
>>>>able to assign them IP addresses 10.120.5.100 - .180.
>>> 
>>> Yes, see the list archives, and 'man dhcpd.conf' looking for classes 
>>> and subclasses.
>>> 
>>> Very briefly, you define a class which matches on some criteria (such 
>>> as the UID starting with ASYNC), then define a pool and only allow 
>>> members of the class to use that pool.