DHCP failover and fixed-address

John Wobus jw354 at cornell.edu
Mon Mar 3 19:27:24 UTC 2008

On Mar 3, 2008, at 5:26 AM, Sebastian Hagedorn wrote:
>> FOr newer releases you may be thinking of reserved leases.
> Yes, that's what I meant.
>> While these
>> seem to work, the only way to enable them is by editting the leases
>> file or a complex omapi interface.
> So what advantage do they offer?

A lease given to a client via a reserved lease is recorded in the
leases file.  By looking at the leases file, you can see what is 

With a statically-configured host, you save the server the trouble
of dealing with the leases file, etc. for all such clients.  As was 
out, in a redundant configuration, you do not even need to coordinate
between the servers regarding the client and its lease.

But if you are on a server and need to know whether some IP address
is leased and when the lease expires, you don't have that information
gathered in the leases file for your perusal.  However, you can
figure it out from logged information: wherever the log shows an ACK, 
using the
configuration and your knowledge of how the ISC server works, you can 
how long a lease must have been given to the client at that point.  I 
think it
might be possible to configure the server to include the lease time in
the log.

There may also be other interesting information saved in the leases
file about the client.  For statically configured hosts, that won't be
available to you.

John Wobus

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