DHCP Lease Renewal Problems

[ncliff]

Hi,

Can anyone help. I have a problem which doesn't occur very often but nonetheless has occurred a few times.

When PC's are coming to the last few days of their IP address lease, they will check with the DHCP server that the lease can be renewed and will either keep the same address or re-negotiate for a new one. I have a Cisco 1750 running DHCP server and I have had several users complain of a message saying:

The DHCP client could not renew the lease of the ip address (x.x.x.x). Your lease is valid until 17 Novemeber , DHCP will try to renew the lease before it expires.

According to the documentation on CCO, the router can choose to remain silent OR send an acknowledgement if the lease is for the same IP address.

Anybody any ideas as to why this message is appearing on the PC's and how to solve it?

[m.singer]

Take a look at this page:

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a00800f0804.shtml#13

[everettdavis]

I have encountered some DHCP related issues when spanning tree protocol was enabled on Cisco switches without portfast on.

When a device would try to renew a lease, the delay introduced in the switch port without portfast on exceeded the timeline DHCP needed to complete and renew the lease. This may not be your issue, but it is worth a look to eliminate it as a possible source.

Be careful with portfast.... research what Cisco warns you about when using it.

Make certain you are dealing with a PC or a Server. Research your network to make sure you don't have devices that will be adversely affected by portfast being turned on. If you do, you can only enable portfast on specific ports which can be near impossible to manage intelligently.

My envionment has GBIC's and fiber links between the remote switch and core switch with no hubs etc. I was able to turn on portfast on each Cat5 port on every switch. The problems I had with DHCP renewals vanished when I did.