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

[Simon Kelley]

In DHCPv6, the unique identifier for a client is NOT the MAC address, 
it's a client ID which sometimes contains the MAC address.

I suspect that dhclient is using the exact same client-id for each 
trial, and just renewing the existing lease. You will need to delete all 
the dhclient state after killing the process.

Simon.


On 23/05/2023 08:43, Linyih Teng 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 <mailto: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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