failover - reserved address

Simon Hobson dhcp1 at
Thu May 21 08:52:12 UTC 2009

Pavel Mlãoch wrote:
>Sorry for this question, but I don't found any 
>solution for reserved leases in my case. When I 
>use reserved leases, I cannot say which 
>configuration may server sent to client. I'd 
>like create leases file by hand (script), but I 
>must say what subnet or router may be used, 
>because in static IP addresses we have denied 
>client with unknown MAC address and this we have 
>to in leases too. I think the best way is 
>declare two subnets, one with right router for 
>known clients and second with wrong router and 
>another subnet for unknown.

Well you could continue using host declarations 
with fixed-address statements. With that, you can 
use "deny unknown-clients" to prevent unknown 
clients getting an address from your servers. You 
do NOT need failover for this, it's OK to have 
two or more independent servers offering a 
service using such fixed address statements - 
provided they all have the same config !

If you went to reserved leases, then I could see 
a couple of ways to do what you want.

One is to use reserved leases to tie clients to 
addresses, but still use host declarations 
(without fixed-address statemets) to make the 
clients "known".

The other might be to use reserved leases, but 
size the pool so that there are no free leases to 
give to unknown clients. This might not work very 
well with failover which really needs a few spare 
leases or they get into a "fight" over them.

Simon Hobson

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