static clients: how log hostnames and create lease entries?

[Glenn Satchell]

>Date: Sun, 27 Dec 2009 03:00:26 +0100
>From: Frantisek Hanzlik <franta at hanzlici.cz>
>
>Glenn Satchell wrote:
>>
>>> Date: Sun, 27 Dec 2009 02:08:10 +0100
>>> From: Frantisek Hanzlik<franta at hanzlici.cz>
>>>
>>> Glenn Satchell wrote:
>>>> Hi Frantisek
>>>>
>>>> One other possibility is to offer a *really* long regular lease, like 1
>>>> or 2 years. It will effectively be the same as a static lease, but will
>>>> be a dynamic lease and go through all the dynamic lease things, like
>>>> dhcpd.leases, but without worrying about the hassle of reserved leases.
>>>>
>>>> group {
>>>> 	# 1 year in seconds
>>>> 	min lease-time 31536000;
>>>> 	host "host1" { hardware ethernet x:x:x:x:x:x ; }
>>>> 	host "host2" { hardware ethernet y:y:y:y:y:y ; }
>>>> 	...
>>>> }
>>>>
>>>> or you could do a similar thing with a class and sub-class, note the
>>>> leading 1 which means media type ethernet.
>>>>
>>>> class "really-long" {
>>>> 	match pick-first-value (option dhcp-client-identifier, hardware);
>>>> 	# 1 year in seconds
>>>> 	min lease-time 31536000;
>>>> }
>>>> subclass "really-long" 1:x:x:x:x:x:x;
>>>> subclass "really-long" 1:y:y:y:y:y:y;
>>>>
>>>> regards,
>>>> -glenn
>>>>
>>>>> Date: Sat, 26 Dec 2009 23:42:14 +0100
>>>>> From: Frantisek Hanzlik<franta at hanzlici.cz>
>>>>>
>>>>> Simon Hobson wrote:
>>>>>> Frantisek Hanzlik wrote:
>>>>>>
>>>>>>> I there some way how, for host declarations with static addresses, do:
>>>>>>>
>>>>>>> 1) log client hostname (which client sent in DHCPREQUEST or DHCPDISCOVER
>>>>>>> as option 12 ) ?
>>>>>>>
>>>>>>> 2) so that they appear in lease file ?
>>>>>>
>>>>>> I don't think so.
>>>>>>
>>>>>> However, if you converted to use reserved leases then the clients get
>>>>>> 'real' leases which go through the normal lifecycle, appear in the
>>>>>> leases file, and get DNS updates/deletes etc - the only difference from
>>>>>> a normal lease being that a reserved lease will never be re-allocated to
>>>>>> another client. I think you need version 4 for this functionality, and I
>>>>>> don't know how well it's documented. I believe you need to manually add
>>>>>> "reserved" as a keyword in an existing lease (or create a new skeleton
>>>>>> lease with this) to uset he feature - and of course, that means stopping
>>>>>> the server while you edit the leases file.
>>>>>
>>>>>
>>>>> For now I have solved (but not sure when it's optimal) point 1) with
>>>>> custom logging defined in global section as this:
>>>>>
>>>>> ----
>>>>> on commit {
>>>>>     if (static){set isst = "static";} else {set isst = "dynamic";}
>>>>>     log (info, concat (
>>>>>       "COMMIT IP,", binary-to-ascii (10,8,".",leased-address),
>>>>>       ",MAC,", suffix (concat ("0", substring(binary-to-ascii (16, 8, ":",
>>>> hardware), 2, 17)),17),
>>>>>       ",hostname,", option host-name,
>>>>>       ",host-decl-name,", pick-first-value(host-decl-name, "(none)"),
>>>>>       ",dhcp-client-identifier,",
>>>> pick-first-value(binary-to-ascii(16,8,"",option dhcp-client-identifier),
>>>> "(none)"),
>>>>>       ",vendor-class-identifier,", pick-first-value(option
>>>> vendor-class-identifier, "(none)"),
>>>>>       ",agent.remote,", pick-first-value(option agent.remote-id, 
"(none)"),
>>>>>       ",agent.circuit,", pick-first-value(option agent.circuit-id, 
"(none)"),
>>>>>       ",leasetime,", binary-to-ascii (10,32,"",encode-int 
(lease-time,32)),
>>>>>       ",asstype,", isst
>>>>>       )
>>>>>     );
>>>>> }
>>>>> ----
>>>>> This produces (in addition to usual) log items as:
>>>>>
>>>>> Dec 26 23:29:56 ns dhcpd: COMMIT
>>>>
>> 
IP,192.168.1.250,MAC,00:20:ed:72:fb:5f,hostname,q,host-decl-name,janusa,dhcp-cli
>>>> ent-identifier,1020ed72fb5f,vendor-class-identifier,MSFT
>>>> 
5.0,agent.remote,(none),agent.circuit,(none),leasetime,216000,asstype,static
>>>>>
>>>>> which is quite sufficient for me.
>>>>>
>>>>> This don't need any additional requirements, but it not solve point 2).
>>>>> I have DHCP v4.0 or 4.1 servers (Fedora 10 - Fedora 12 machines), but
>>>>> manually edit lease file seems little crazy for me.
>>>>> "infinite-is-reserved On" dhcpd.conf statement isn't answer, because
>>>>> as far as I understand man page, client itself must request infinite
>>>>> lease time - which isn't realistic.
>>>>> dhcpd.leases man page in addition to "reserved" mention also "bootp"
>>>>> flag, but again without any details.
>>>>>
>>>>> Then, I still not know, when there is any elegant way how put fixed
>>>>> address hosts to dhcpd.leases file. I do not need any dyndns updates etc.
>>>>>
>>>>> Any advice?
>>>>>
>>>>> Thanks, Franta Hanzlík
>>>
>>> Hello Glenn,
>>>
>>> Your concept would be fine, but how then is possible assign fixed IP
>>> address to these hosts? When I use "fixed-address" statement, then these
>>> hosts not appear in dhcpd.leases, as there are only dynamically assigned
>>> ones, I'm right? Or is other way how tight assign for given hardware
>>> ethernet address given IP address?
>>>
>>> Regards,
>>> Franta Hanzlík
>>
>> Ah, yes, I see what you mean. You won't know in advance what the IP
>> address will be, but once the PC is given a dynamic address then it
>> won't change. If you use a 1 year lease, then at around 6 months the PC
>> will try and renew for another 1 year.
>>
>> If you need to lock it down then you could create separate pool(s) with
>> a specific range of IP addresses, eg something like this:
>>
>> subnet 192.168.1.0 netmask 255.255.255.0 {
>> 	...
>> 	pool {
>> 		deny members of "really-long";
>> 		range ...
>> 		...
>> 	}
>> 	pool {
>> 		allow members of "really-long";
>> 		# treat this range like fixed addresses
>> 		range 192.168.1.20 192.168.1.30;
>> 	}
>> }
>>
>> regards,
>> -glenn
>
>Ah so, I understand this idea, and its seems reasonable. I use Your
>reccomendations. Many thanks!
>
>But anyway I cannot get on, why, in powerfull ISC dhcpd with tons of its
>options, is so hard solve this problem. I don't well understand all of
>aspects about it, but I like idea of dhcpd.leases database with all
>controlled hosts.

I think it was an optimisation that was done in a very early version,
maybe 2.0? The idea was that a host with a fixed-address didn't need to
store or process the lease state information as the server would hand
out the same fixed IP address for every request from that client.

I think reserved leases are meant to provide the facility you need, but
as yet there is no easy way to configure that in dhcpd.conf. It would
be nice if you could set up a class, pool or host statement and specify
'reserved' in that context perhaps?

regards,
-glenn