config help - scaling problem

Jerimiah Cole jcole at
Wed Mar 3 00:09:48 UTC 2010

Marc Perea wrote:
> We've had a lot of problems in years past with dhcp protocol failover, 
> mostly communications interrupted and all leases owned by peer, so we're 
> currently using a warm standby with frequent backups of the .conf. As 
> noted, we really don't care about the actual state of the lease, so we 
> don't even really need the .leases file at all except for the operation 
> of the server.

Me too.  The strategy is to monitor carefully and put processes in place 
to respond before service degrades.  You'd have to do this anyway with 
failover in place.  We chose to avoid the additional complexity of failover.

> Since all of our environment comes from the .conf and not the .leases, 
> does anyone see any reason why we shouldn't have 1 or more other servers 
> also performing active dhcp servicing (as was recommended)? If I were to 
> point my relays to several DHCP servers, it seems I'd have more 
> redundancy and failover without having to use any protocol, which is a 
> benefit in my mind. Any flaws in that thinking?

I don't think this will work with the class-based config because the 
state data would affect how the server would respond.  All servers would 
have a different view of the state of the client's lease.

However, this exactly how I have 4.2.0a1 configured in my lab right now 
with the host based config and it works perfectly.

> alleviate this particular problem in environments like mine. It sounds 
> like I would like to use both the delayed fsync() and host option 
> matching - is there a release that supports both of these? From David's 
> reply, I'm inclined to think that 4.1.1+ has delayed fsync(), and 4.2+ 
> has host option matching, but 4.2+ has a bug that breaks the former. Is 
> that right, or is it just broken with failover?

With the host based config, there is no state data to write to disk, so 
the delayed disk writes aren't necessary.  In fact, on my test platform, 
there are about a dozen "active" clients, but the leases file is 
completely empty.


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