static clients: how log hostnames and create lease entries?

[Glenn Satchell]

>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