Migrating from a Cisco Routers DHCP to ISC DHCP
Kai.Zemke at smartnet.de
Tue Oct 20 08:29:03 UTC 2009
These are quiet interesting approaches.
I'll keep them in mind and will discuss about them with my colleagues in the next meeting.
Is it also worth thinking about migrating the existing lease database from the router to the "dhcpd.leases" file? Something like parsing the routers complete binding table and construct a leases file with this information?
I have a list that keeps the following information:
IP address Client-ID/ Lease expiration Type
Some.ip some.mac.adress Oct 24 2009 11:44 PM Automatic
At the first view I think this information might be exportable to a leases file. Anyone tried something like this before?
Von: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] Im Auftrag von Simon Hobson
Gesendet: Montag, 19. Oktober 2009 14:41
An: Users of ISC DHCP
Betreff: Released from eSafe SPAM quarantine: Re: Migrating from a Cisco Routers DHCP to ISC DHCP
Zemke, Kai wrote:
>One thing I'm thinking of is the question: is there a way to keep
>the old ip dhcp binding table from the cisco router? And maybe copy
>it to the isc dhcp server?
>Or what ways are pefered to make all clients get a new ip address on
>the new server. So that there are no adresses on the net twice
>because the lease hasn't expired yet
>but the server offered this ip to a new client because he just
>wasn't aware of an old lease.
There are several ways to do this, what will work for you depends on
your network and clients.
One technique would be to shorten the leases on the old server -
working progressively in stages until you are down to a few minutes.
Then at a quiet time turn off the Cisco server, wait for the
configured lease time, and turn on the new server. All clients will
see a network outage as their leases expire, but will then renew with
the new server. For most clients, they will get their old address
back - they'll request it from the server and since it should be free
then that address will get assigned by the new server.
Another technique would be progressively reduce the size of the pool
(IIRC add to the excluded address range(s)) on the Cisco server, wait
for the leases to expire, and then add those addresses to the new
server. Any clients with addresses in the bit of pool that you chop
off will be forced to get new leases - either different addresses
from the old server, or from the new server. Over time you can force
all the clients over to the new server. You can speed things up by
cutting down lease times on the old server in advance, and minimise
impact by timing the alterations so that leases will expire during
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