[Kea-users] i do not understand the concept of shared networks

Giso Kegel giso.kegel at cloud.ionos.com
Wed Mar 11 13:40:37 UTC 2020


Hi Cathy,

thank you for your time and that description.

The most important sentence here is that
"...In all of the above, there is no mention of Host Reservations..."
for me it is exactly the use case that almost all the subnet definitions 
are host reservations.

The second point is
"... it doesn't matter which subnet provides the address to a client, 
any/all should work just fine. ..."
That's the point a server should only get an IP from his specific 
network via host reservation.

That means i do not need Shared Networks!?

Am 11.03.20 um 12:31 schrieb Cathy Almond:
> On 10/03/2020 13:14, Giso Kegel wrote:
>> Hi Folks,
>>
>> I work with kea 1.6.1
>>
>> I really do not understand the concept or at leased the documentation
>> regarding shared-networks.
>> Do i need shared-networks or not?
>> I do not have the problem that I have networks that grew out of there
>> original definition.
>>
>> https://kea.readthedocs.io/en/latest/arm/dhcp4-srv.html
>>
>> lets say i have 50+ subnet4 that will ask the kea dhcp server over dhcp
>> relayhosts (a swtich).
>>
>> All these subnet4 will hold only server that have a IP-reservation.
>>
>> Do i need multi shard networks?
>> Can or do i have to put these 50+ networks in multi shared networks?
>> Do i have to use different interfaces  for each shared network?
>>
>> I would be very thankful for some enlightenment.
>>
>> Best
>> Giso
> What are shared-networks (and do you need to use them or not)?
>
> They're a way to tell the DHCP server that all of the subnets specified
> inside that one shared-network can be considered equal - IP routing of
> clients should not be broken if you give any client requesting an
> address, any IP address from any of the included subnets.
>
> That's the very simple case - and it's pretty clear that if you ran out
> of addresses for a specific site and needed to add a new subnet for it,
> running over the same wire and sharing the same local relay, that this
> is a primary use case for shared-networks - it doesn't matter which
> subnet provides the address to a client, any/all should work just fine.
>
> But there is more to this.  Clients in a shared-network are those who
> all reach the DHCP servers via the same route - be it a local interface,
> or, more likely, the same relay.  Consider the case of cable modem
> provisioning where different types of 'client' will request addresses -
> all via the same relays, but with the need to distinguish between them
> and allocate them to different subnets.  Typically it will be possible
> to separate clients by means of Classification and then use this to
> restrict clients within a shared-network to the subnets that they should
> be using.  This is the second, and slightly more complex use case.
>
> The basic principles are therefore:
> - all the clients are reaching the DHCP server via the same local relays
> (or are local to it)
> - unless classification is added, it's OK for a client to get an address
> from any subnet within the shared-network.
>
> (And in all of the above, I have pretended that host reservations don't
> exist.  They can and will of course change how addresses are allocated
> to clients, but having got the basics on shared-networks and
> classification, now reading the documentation on what's different when
> there are also host reservations to consider should be a bit easier...)
>
> Cathy
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-- 
Giso Kegel




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