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high performance open source DHCP solution?



We've recently setup ISC DHCPd with failover for lease information, and 
LDAP as a configuration source (mostly because of our need for 
dynamically adding dhcp reservations for cable modems, etc) -- we don't 
have any performance issues thus far, but I'd imagine in a failover 
environment, it might be safe to consider a ramdisk for leases.  
Obvoiusly breaks RFC2131, but...

Walter Keen
Network Engineer
Rainier Connect

(P) 360-832-4024
(C) 253-302-0194


On 07/20/2011 03:28 PM, Jimmy Hess wrote:
> On Wed, Jul 20, 2011 at 9:31 AM, Nick Colton<ncolton at allophone.net>  wrote:
>> We were seeing similar issues with low leases, moved the dhcpd.leases file
>> to a ramdisk and went from ~200 leases per second to something like 8,000
>> leases per second.
> Yes, blame RFC2131's  requirement that a DHCP server is to ensure that any
> lease is committed to persistent storage, strictly before a DHCP
> server is allowed to
> send the response to the request;   a fully compliant DHCP server with
> sufficient traffic
> is bound by the disk I/O rate  of underlying storage backing its database.
>
> I do not recommend use of a RAMDISK;  it's safer to bend the rule than break it
> entirely;   a safer way is probably to use a storage system on a battery-backed
> NVRAM cache  that you configure to ignore SYNC() and lie to the DHCP server
> application,  allowing the storage system to aggregate the I/O.
>
>
> Of course,  committing to a RAMDISK tricks the DHCP server software.
> The danger is that if your DHCP server suffers an untimely reboot, you
> will have no transactionally safe record of the leases issued, when the
> replacement comes up, or the  DHCP server completes its reboot cycle.
>
> As a result, you can generate conflicting IP address assignments, unless you:
> (a) Have an extremely short max lease duration  (which can increase
> DHCP server load), or
> (b) Have a policy of pinging before assigning an IP, which limits DHCP server
> performance and is not fool proof.
>
> --
> -JH
>
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