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Today's Topics:
1. Re: Shared DHCP pool for multiple VLAN interfaces (Simon)
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Message: 1
Date: Thu, 25 Nov 2021 17:04:28 +0000
From: Simon <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Shared DHCP pool for multiple VLAN interfaces
Message-ID: <764b18cb-4002-4b38-a511-790394b11...@thehobsons.co.uk>
Content-Type: text/plain; charset=utf-8
Fabian Druschke <fabian@knogle.industries> wrote:
> Now i'm facing an issue which doesn't seem to be that simple.
>
> In my network topology i got a bunch of different VLANs, VLAN 405-480, and
> VLAN 700-750.
>
> The DHCP server should serve leases to requests, coming from these
> interfaces. But they should share a single DHCP range only, 10.20.0.0/16.
>
> Is it possible to accomplish this goal, serving DHCP leases on all these VLAN
> subinterfaces, and serving DHCP leases for this single subnet?
The short answer is ?it depends? !
The fuller answer is probably not very short at all.
The first thing you need to clarify is the network topology - just saying ?I
have VLANS? is no more informative than ?I have a number of LANS?.
Specifically, how are they connected, how is the addressing done, and most
importantly how do you differentiate traffic and route it to the correct VLAN ?
I ask the latter as your question makes it sound like you have a number of
separate networks (VLANs), all sharing the same IP subnet (10.20.0.0/16).
That?s a tricky one to pull off reliably. I can see a situation where (e.g.) a
host with address 10.20.10.20/16 in VLAN 405 talks via a router at 10.20.0.1/16
to communicate with another host at 10.20.10.21/16 which also talks via a
router at 10.20.0.1/16. As general IPv4 addressing goes, that just isn?t going
to work - principally because IPv4 doesn?t have the concept of on-link and
off-link prefixes like IPv6 does, and hence the two devices would not know they
needed to go via the router to talk to each other. Unless the router does a lot
of proxy-ARP which itself could be interesting with that size of network.
So more information needed before anyone can usefully answer your query.
Simon
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