[cisco-voip] DHCP Migration Strategy - RFC

[Fuermann, Jason]

If I remember correctly we’ve had leases set to 30 minutes before without any issues. I wouldn’t go below that because the phone is going to be renewing at a 15 minute interval. I’d check on what DHCP server you’re using, some will check if an address is in use before issuing one (at least I’ve experienced that on windows DHCP), and on that same note, make sure there is enough overlap in the scopes so you don’t run out of leases due to addresses being blocked for conflicts.

From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Wes Sisk
Sent: Thursday, September 17, 2009 4:03 PM
To: Lelio Fulgenzi
Cc: cisco-voip voyp list
Subject: Re: [cisco-voip] DHCP Migration Strategy - RFC

depending on your nw topology this could still be a problem:
CSCso60222    After DHCP Monitor service is stopped, IP is given to DHCP clients

make sure DHCP DISCOVER (and renew as a subset of DISC) will not reach the CM server.

Phones tend to go haywire when lease duration goes below something like 5 minutes so I would stay very clear of that on the order of 1 hour.  I don't have the bug for that handy.

/Wes

On Thursday, September 17, 2009 4:51:28 PM, Lelio Fulgenzi <lelio at uoguelph.ca><mailto:lelio at uoguelph.ca> wrote:

So, I'm planning on moving the DHCP service off a CallManager subscriber to our central DHCP service. Past experience tells me that this shouldn't be too much of an issue, but there are some things to look out for. For example, IP address conflicts on phones causes both phones to reset.

Here's what I'm planning on doing (testing out on one scope to begin with):

 1.  Lower lease time on CallManager subscriber DHCP server from 8 days to 1 hour. Wait until all phones have a 1 hour lease.
 2.  Change IP helper address on interface to new DHCP server.
 3.  Deactivate scope on CallManager subscriber DHCP server.
 4.  Wait one hour until all phones have new lease on new DHCP server and all IP address conflicts are resolved.
 5.  Remotely reset phones that are not co-operating.
Two questions:

 *   Is having a 1 hour lease time on the subscriber an issue? It's a 7835 from about 4 years ago and it does nothing else other than DHCP/TFTP.
 *   Can I go a step further and lower the lease time to 30min or even 15 min without significant concern?
We have about 7500 phones.
---
Lelio Fulgenzi, B.A.
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
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"Bad grammar makes me [sic]" - Tshirt






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