different devices getting the same ip address

[dorian]

It is a matter of the moment when you are starting to read a long mail
containing discussion.

Of course, if you are starting read it in the middle it can be annoying.
But when you want to read only new opinions much more annoying for me is
scrolling down the whole content to find out where is something new and
really interested for me.
Especially when I am using mobile.

So forgive me but in my opinion top-posting is much more functional in
this time.

Rgds,
Dorian


Simon Hobson wrote:
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
>
> dorian wrote:
>
>> Since I am registering (with another tools) all the IPs in the network I
>> know that there number of different IPs assigned (whenever) by DHCP
>> server is only 30924 which is significantly less than theoretically
>> possible 262142.
>>
>> I have around 1000 users per day at the hotspot system. Some of them are
>> the same users some are 'accidental' ones.
>>
>> The config lease times are following:
>> default-lease-time 86400;
>> max-lease-time 86400;
>> which means 24h
>>
>> Since working hours of the hostpot are 8:00 - 22:00 and lease time is
>> 24h and the number of users is ~1000/day  I do not understand why
>> sometimes a host obtains IP address being in use.
>
> Have you looked at the leases for these duplicate IPs ? The answer
> given to the OP was that the IP was leased to two "different" devices
> because as far as DHCP is concerned, they are the "same" client
> because they have the same Client ID.
>
>> BTW: the current dhcpd.leases file contains 503007 entries  (entries not
>> lines)!
>> Does it mean the file contains whole 'history' of the leases whenever
>> given? What for?
>
> Firstly, the leases file is a "log database" where updates are
> performed by writing a new record at the end o the file - this makes
> it fast and easy to do "safe" updates which are easily (and cheaply)
> synced to disk as required by the RFCs. Thus an active lease may have
> more than one entry - the last one is the correct version.
> To counter the file growing indefinitely until disk space is
> exhausted, it is rewritten periodically (every hour unless you change
> the code and recompile) with a fresh copy - at which point there will
> be exactly one record per lease.
>
>
> The second feature is that every lease ever given out is kept until
> such time as the address is re-used. Thus, if you had 1000 users one
> day, then a different 1000 users/devices the next day, you'd have 2000
> leases in the database. This too is required by the RFCs which specify
> that as far as is possible, a device should be given an address
> previously leased to it. Note that some other DHCP servers do not do
> this.
> it sounds like you have a high churn rate, and so lots of new users.
> Each of these will still have a lease recorded.
>
> If you wanted to override this, then there are a couple of things you
> could do.
> One is to stop the server, and write a script to clean out old records
> from the leases file.
> Another is to "rotate" the pool periodically. When the server starts
> up, any leases not within a defined range will be deleted. Thus if you
> had a range of say 172.16.8.0-172.16.255.255 one week, and the next
> week changed this to 172.17.0.0-172.17.255.255 then all the leases in
> the 172.16.n.n bock would get deleted.
>
>
> And on this, there is a performance issue you might wish to be aware
> of. On startup, the server will create in-memory records for every IP
> address in every range defined. Thus in your case, you are creating
> tables to track over half a million addresses - while your requirement
> seems to be only around 1000 per day. Memory requirements and startup
> times would be improved by creating a range that's better sized to
> your requirements - a few (tens of) thousands would seem more
> appropriate.
>