Computers losing IP address

At one of our sites, computers loses there IP address whenever there is an outage, which is caused by power failure, or service disruption, now this site is on two floors, and only one of the floor computer looses IP (Tech at site reboots all switches, and computers get IP again), so I am assuming there would be something wrong on the switch? what things I should be checking/fixing to find the source of the issue?
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LeoAsked:
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AkinsdNetwork AdministratorCommented:
It looks like the switch may dropping DHCP discovery packets even though ip helper-address is properly configured.
This may be a result of memory leak, or OS corruption or TCP State denial of service manipulation.
See the link below for more information on the latter
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20090908-tcp24 
I copied and pasted the workaround section of the advisory below
Workarounds

It is possible to mitigate these vulnerabilities with the following workarounds.
Cisco IOS Software

The Cisco Guide to Harden Cisco IOS Devices provides examples of many useful techniques to mitigate against the TCP state manipulation vulnerabilities. These include:

    Infrastructure Access Control Lists (iACL)
    Receive Access Control Lists (rACL)
    Transit Access Control Lists (tACL)
    VTY Access Control Lists
    Control Plane Policing (CoPP)
    Control Plane Protection (CPPr)
    Management Plane Policing (MPP)

To fix the former, try upgrading or reloading the OS, or replace the memory
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LeoAuthor Commented:
so try upgrading/reloading the OS... its a domain controller...and its on VMware, virtual machine.
I had a look at event viewer of DC, there was nothing obvious there, should I enable logging on switches, and when it looses IP next time, It can give an idea?
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AkinsdNetwork AdministratorCommented:
On the switches (Cisco IOS) not the server
Sorry for the ambiguity

Everything I posted previously refers to the switches.
Your switches are most likely L3.
DHCP discovery packet drop issues is more common with L3 compared to L2. If you have dedicated distribution switch, may I suggest using L2 switches for your access layer.
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arnoldCommented:
How many DHCP servers/distributors do you have in the environment and if only one, that could explain the issue. A remedy to extend the time is to make sure the lease time of IPs is not too short.
A short lease time, means the Computers must renew their Ips , that might lead to a dos on the DHCP server/possibly locking that out.
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AkinsdNetwork AdministratorCommented:
Also make sure that your distribution switch is the root bridge.
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