[Dnsmasq-discuss] dhcp-lease-max is only for DHCPv4?

[Eric Fahlgren]

Here's some details on what Simon is talking about, the DHCP DUID:

https://www.rfc-editor.org/rfc/rfc3315.html#page-19

I was wondering if the dhclient was releasing when it dies at step #4?
 Maybe just background it and keep running more clients?

I would definitely try @imnozi's suggestions, especially the one of
trying smaller values for the limit.


On Tue, May 23, 2023 at 1:15 AM Linyih Teng <tenglinyih at gmail.com> wrote:

> For the test.. i'm just curious, there is no other reason.
>
> However, On the client side, I wrote simple scripts to run the dhclient,
> and this script will sequentially run 512 dhclient.(the number 512 is not a
> magic value, other values will happen same situation.)
>
> steps of the script:
>
> 1. create macvlan interface(It will make different MAC address for clients)
>
> 2. run dhclient with macvlan interface
>
> 3. get an IP from DHCPv6 server
>
> 4. kill the dhclient and remove the macvlan interface
>
> 5. back to step 1. and go on.
>
>
> Results:
>
> After scripts, if the 513th client comes, the server will serve the IP to
> the 513th client.  but it is not just lease max + 1 th client getting
> this issue, all after the 512th client can get IP from the server.
> At this time,  the lease entries are remaining at 512, and all after
> clients will not appear in the lease file.
>
>
>
> Thanks,
> Lin
>
>
>
> Geert Stappers <stappers at stappers.nl> 於 2023年5月23日 週二 下午1:59寫道：
>
>> On Tue, May 23, 2023 at 12:05:08AM +0100, Simon Kelley wrote:
>> > On 22/05/2023 12:18, Linyih Teng wrote:
>> > > In the manual page is written:
>> > > > -X, --dhcp-lease-max=<number>
>> > > >        Limits  dnsmasq  to  the  specified  maximum number of DHCP
>> > > >        leases. The default is 1000. This limit is to  prevent  DoS
>> > > >        attacks from hosts which create thousands of leases and use
>> > > >        lots of memory in the dnsmasq process.
>> > >
>> > > Hello,
>> > >
>> > > I'm using dnsmasq2.89 and testing the maximum lease count of the
>> DHCPv6
>> > > server with the *dhcp-lease-max* option.
>> > >
>> > > For the testing, I'm using below configuration:
>> > >
>> > >     *dhcp-lease-max* = 512
>> > >     *dhcp-range*=tag:pool0,2022::1,2022::1f:ffff:ffff:fffe,64,120m
>> > >     tag-if=set:pool0,tag:intfv0
>> > >
>> > >
>> > > However, when the number of clients reaches the maximum number, the
>> > > server still provides IPs to clients. Is this the expected behavior of
>> > > DHCPv6?
>> > >
>> > There's a possible difference between the number of clients and the
>> number
>> > of DHCP leases, since leases can expire to be deleted by the client.
>> >
>> > Are you saying that the number of simultaneous DHCP leases increases
>> without
>> > bound, or that the 513th client gets a lease? Have you checked the
>> number of
>> > leases in the dnsmasq.leases file?
>>
>> Original Poster has yet to say what the expected behaviour should be.
>>
>> Thing I am saying: Why limit dhcp-range by dhcp-lease-max?
>>
>>
>> Regards
>> Geert Stappers
>> --
>> Silence is hard to parse
>>
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