Question about DHCP.
dhcp1 at thehobsons.co.uk
Mon Jul 7 22:10:14 UTC 2008
Luis Fernando Lacayo wrote:
>I have two DHCP servers (dell 2950 with 2 CPU's and 4G or RAM) set up as
>I had a subnet that had ran out of available leases and I had to clear
>the old leases. I stopped but DHCPD servers and deleted both of the
>lease files on each of the two servers.
>any advice is welcomed.
That was (IMHO) a pretty dumb thing to do, and may well cause you
much grief in the future - depending on your network, client churn
rate, and lease times.
You now have a situation where your DHCP servers do not know what
promises they made, and they will be at liberty to try and allocate
leases to any new devices coming onto the network for addresses that
are already in use. When this happens, the address will be marked as
abandoned if the current device responds to pings. Thus you may well
end up with abandoned addresses.
Further, as devices come up to renew their leases, if the address has
been marked abandoned then IIRC the server will NACK the request and
force the client to get a new one. Given the number of addresses in
use (to exhaust the address pool, I assume you have a number of
clients close ot the size of the pool), there is a good chance that
further addresses will be marked as abandoned.
Abandoned addresses are only retried as a last resort, so the result
could be that you end up with no free leases and a high churn rate.
On the other hand, if no new devices appear, then the servers will
populate their lease databases as the clients renew.
A second problem awaits you if you have been using dynamic DNS, since
you have deleted the records of what DNS entries the DHCP servers
have created. You can expect more fun with stale entries from that.
In future, should this happen again, I would suggest that you simply
delete some old leases (assuming you are sure the devices are no
longer on the network).
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