[Dnsmasq-discuss] Reading the dhcp.leases file

Reddeiah Raju Konduru raju39k at gmail.com
Tue Feb 14 18:50:23 GMT 2017


Sorry wrong Thread.

On Tue, Feb 14, 2017 at 10:48 AM, Reddeiah Raju Konduru <raju39k at gmail.com>
wrote:

> Hi Simon,
>
> Thanks for the DHCP Client-ID's patch.
>
> - Raju
>
>
>
> On Tue, Feb 14, 2017 at 7:10 AM, Simon Kelley <simon at thekelleys.org.uk>
> wrote:
>
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>> Albert's suggestions are good, and you can't reliably read the leases
>> file - in gets modified by delete-and-rewrite, so if the timing is
>> wrong, you'll see an incomplete write.
>>
>> DHCP script gets all the information needed to maintain a database
>> equivalent to the leases file, using whatever engine you prefer.
>>
>>
>>
>> Cheers,
>>
>> Simon.
>>
>>
>> On 12/02/17 05:53, Albert ARIBAUD wrote:
>> > Hi Sam,
>> >
>> > Le Sat, 11 Feb 2017 16:06:55 -0600 Sam Weber <samweber01 at gmail.com>
>> > a écrit:
>> >
>> >> In our system, when a change occurs to the DNS entries we want
>> >> dnsmasq to respond to, we scan the directory of active entries
>> >> and then grep the dhcp.leases file to see if the entry exists
>> >> there.  If the entry is not found in the leases file, we omit it.
>> >> Once the scan and check is completed, we write a new hosts file
>> >> and then send SIGHUP to dnsmasq so it knows to read the new file.
>> >> This works well most of the time.  Sometimes, however, a
>> >> perfectly valid entry is not found in the dhcp.leases file so we
>> >> incorrectly omit the entry from the dnsmasq hosts file.  We can
>> >> see that the leases file gets written very often in our system,
>> >> and we think that sometimes we must be reading the leases file
>> >> whilst dnsmasq is writing it, resulting in our reading the file
>> >> when a value of interest has not yet been written.  Is this idea
>> >> of our sometimes reading an incomplete leases file a possibility?
>> >> Is there a workaround other than reading the leases file several
>> >> times?
>> >
>> > Not sure I understand your problem right, so I'll rephrase it and
>> > let you tell me if that's what you do and want to happen:
>> >
>> > - you have a list of names associated with IP addresses;
>> >
>> > - you want to filter this list, keeping only the entries where the
>> > IP address is currently being leased;
>> >
>> > - you want the filtered list to be used by dnsmasq in its name
>> > resolution process.
>> >
>> > - you want the list to be kept up to date with the current leases.
>> >
>> > - IOW, you want DHCP clients that get an IP which appears in your
>> > list one to be assigned the corresponding name in the DNS, and you
>> > want the DNS to NOT map names in this list if the corresponding IP
>> > is not leased right now.
>> >
>> > Is that it?
>> >
>> > If so, /maybe/ dhcp-script is what you need or at least can help
>> > you detect when you need to run your update, as it would give you a
>> > sign that the leases just changed.
>> >
>> > But it seems to me what you are doing is not really different from
>> > what dnsmasq already does (i.e. reflexting DHCP names into the DNS)
>> > when the MAC-to-IP mapping is done with static leases and each
>> > dhcp-host line specifies a name.
>> >
>> > If this is indeed what you are doing, then maybe you can achieve
>> > that with options dhcp-hostsfile and dhcp-ignore-names.
>> >
>> > You'd use dhcp-hostsfile to point to your list written as a list
>> > of dhcp-host options, minus the "dhcp-host=" prefix.
>> >
>> > You'd specify dhcp-ignore-names to make sure no host can overrule
>> > your list and choose its own name in its DHCP requests.
>> >
>> > You would then only have to tell dnsmasq whenever your list changes
>> > by sending it SIGHUP, but you would not have to care about DHCP
>> > leases being granted or released, as that is automatically
>> > reflected in the DNS part of dnsmasq.
>> >
>> > HTH (again, IIUC)
>> >
>> > Amicalement,
>> >
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>
>
>
> --
> Thanks & Regards,
>
> Reddeiah Raju Konduru
> +918095133903 <+91%2080951%2033903>
>



-- 
Thanks & Regards,

Reddeiah Raju Konduru
+918095133903
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