Pool independent GI Address
niall.oreilly at ucd.ie
Mon Dec 15 09:59:54 UTC 2014
If I jump in here, Simon can take a well-earned break.
At Mon, 15 Dec 2014 09:57:44 +0100,
Stephan Sanders wrote:
> Hi Simon,
> "Simon Hobson" <dhcp1 at thehobsons.co.uk> wrote:
> > Now I am really confused !
> > Is 10.10.0.0/16 where the client devices live, or where >Server A
> > lives ? From what you wrote earlier it sounded like >the former,
> > this >sounds like the latter.
> Let me explain the solution.
As Simon already suggested, explaining your goals, rather than
jumping ahead to what you see as the "solution" would likely be
> Each domain
I wonder what you mean by "domain".
> is located on a switch/router with a dhcp-relay.
> on each domain are two subnets configures (primary and secondary
> 10.10.1.0/29 primary GI and GW address: 10.10.1.1
> 10.11.1.0/29 secondary GW address: 10.11.1.1
What you don't make fully clear is whether these two prefixes are
used on the same (V)LAN.
> The dhcp relay allows to use more than one dhcp server but only to
> define one GI address.
> So for the first server everything is fine.
I'm not sure why you think so, as you haven't explained here what
purpose you intend for each server.
> The GI address is within the pool.
It's not clear what you think "pool" means. It is crucial to ensure
that the gateway IP address ("giaddr", not "GI address" please) NOT
be included in the range from which client addresses are to be
dynamically assigned. It is a very common mistake to neglect this.
> But the Backup Server
> will receive discovers from the GI 10.10.1.1 and has to offer
> addresses from 10.11.1.0/29.
Simon has suggested a configuration fragment which shows how to
ensure that a server can offer addresses only from the prefix
for which it is responsible.
> Selection of which /29 pool should be done by option82.
What are you trying to achieve? Why are you so sure that option 82
is part of the solution?
It may be useful to explain, without reference to how you expect to
implement it, what your intended criterion is for selecting one or
other prefix as the one from which a client address is to be
> option82 will be filled by the dhcp relay with a string for the
That's possible, but not necessarily relevant to your goals (which
you haven't explained yet).
> > The server will *NOT* try and allocate an address from >anything
> > other than 10.10.0.0 because it doesn't have any >addresses in teh
> > other >subnets to give out. But it will >know that regardless of
> > whether the GI-Addr is in 10.10, >10.11, or 10.20 it can give out
> > addresses in the >10.10.0.0 subnet.
> Thats the way i want run my configuration.
So why not just copy and paste Simon's example, configuring a range
for one subnet on server A, and for the other on server B?
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