Rebuilding Leases file from log file

[Larry Apolonio]

Simon Hobson wrote:

> Larry Apolonio wrote:
>
>> I know its not perfect but is it possible to send dhcp logs to a 
>> remote syslog server and rebuild the dhcp leases file based on mac, 
>> IP address was assigned, and time. I'd use the lease time in 
>> dhcpd.conf to configure the amount of time.  Say the lease time was 1 
>> day then
>>
>> Nov  9 12:24:32 dhcp-server dhcpd: DHCPACK on 10.10.126.164 to 
>> 00:00:00:00:22:95 via 192.168.0.4
>>
>> would become
>>
>> lease 10.10.126.164 {
>>  starts 2 2007/11/09 12:24:32;
>>  ends 4 2007/11/11 12:24:32;
>>  tstp 4 2007/11/11 12:24:32;
>>  binding state free;
>>  hardware ethernet 00:00:00:00:22:95;
>> }
>>
>> What bad mojo would I encounter?
>>
>> Basically would I be able to start up my spare server as the DHCP 
>> server with the dhcpd.conf file using a leases file generated from 
>> the syslog server?
>>
>> Now I can put the leases file in tmpfs or /dev/ram, syslog would be 
>> off the DHCP server, and we would be using something more current 
>> than an hourly rsync of the leases file.
>
>
> Well a while ago Ted suggested something (for cable operators) along 
> these lines. Run a DHCP server in the remote locations (ie closer to 
> the customers), running OS & apps from flash/whatever (ie diskless) 
> and leases in ramdisk. To make the leases persistent, run these in 
> failover with a central server back at the NOC (which of course can 
> have decent performance disks etc), but configured so that only the 
> remote servers normally handle client requests.
>
> If the remote server gets restarted for any reason (such as after a 
> power cut), it will pull the leases from it's peer back in the NOC and 
> carry on as normal.
>
> Might this be easier to implement - it gives you a continuous live 
> backup of the lease states ? Of course, your 'backup' can easily be 
> made into a live server by putting it in partner down mode and when 
> the primary comes back up the leases will be synced and things will 
> revert to normal.

Thanks Simon,

Hows performance in this mode?  Can this handle 100 4-way handshakes per 
second?  I was told that two DHCP servers in peer mode (AKA failover) do 
not perform well.  This is second hand information, so I have not 
confirmed this, thus I have avoided DHCP servers in peer mode and opted 
to rsync the lease and dhcpd.conf file and restart it.  In my research I 
have found that startup times can get really bad, but with two peer DHCP 
servers, it may be moot.

Larry