For all practical reasons, I can't see why you should keep them longer than a month (mostly, a month is too long, seeing how most DHCP leases are only good for a week, and it's usually hijacked DHCP clients who are attacking you). I'd recommend you back up the data just as far as a class C, so you can know who is attacking you generally (where they are attacking from, and when it has happened, generally [ie, week by week breakdown of recurring class C attacks]). If you need help with that, I think I could throw together a quick script that you would run in a cron.

For all practical reasons, I can't see why you should keep them longer than a month (mostly, a month is too long, seeing how most DHCP leases are only good for a week, and it's usually hijacked DHCP clients who are attacking you). I'd recommend you back up the data just as far as a class C, so you can know who is attacking you generally (where they are attacking from, and when it has happened, generally [ie, week by week breakdown of recurring class C attacks]). If you need help with that, I think I could throw together a quick script that you would run in a cron.