|
Question : DHCP lease time /renewal concept
|
|
we have some 13,000 PC using Novell 5.1 servers for DHCP.(2 servers)
our lease time is 7 days. our network got 15 VLAN and a common VLAN (where DHCP servers are in)& WAN .All VLAN got IP forwaders (to forward BOOTP to DHCP server).everything working fine.
As per theory if PC get a IP from DHCP it shd renew by 1/2 of lease.(T1)
If particular DHCP not avilable it should send out (T2) to any server by
87.5 % of lease.(T2).
means
say I got a IP by 01/03/2003 08:00 am ( lease obtained)
expiry is 08/03/2003 08:00 am (7 days )
now the CLient should attempt to renew after 3.5 days(mean 04/03/2003 08:00 pm).
but actually what is happening is client is renewing it's IP for every restart.
say if i restart by 01/03/2003 evening (say 08:00 pm)now hte new settting in ipconfig will be like following
lease obtained 01/03/2003 08:00 pm
expiry is 08/03/2003 08:00 pm (7 days - from the time i restart the PC )
I checked with so many source including novell site. but what novell telling it is NORMAL. see the attached TID from novell.But i dont feel DHCP working shd be this way. I am doing anything wrong in config on server side ? If server side config wrong also this DHCP REQUEST from client which is win2k,winNT,XP .why this is happening ? anything due to IP forwaders (nortel products)? if is due to IP forwarders why it is happening across the WAN also (cisco routers forwarding client request to DHCP)?
Frnds thanks in advance for you valuable comments...
Moorthy..
--------------------
Every time the DHCP workstation is rebooted, it renews the lease. This happens even though
1) the DHCP lease has not expired.
2) the T1 (renewal) time has not been reached.
solutions
Each time the TCP/IP stack is unloaded and reloaded, or if the workstation is rebooted, the DHCP workstation sends a DHCPREQUEST packet to the DHCP server, which causes a reset of the renewal (T1), rebinding (T2), and the lease time. This is normal.
See RFC 2131 for more information.
---------------------------------------------------------------------------
|
Answer : DHCP lease time /renewal concept
|
|
moorthy, what Novell has told you makes complete sense. Let us understand the concept of leasing IP addressed. The idea is to dynamically & OPTIMALLY use the available block IP addresses. So, if a machine is dynamically allocated an IP address (using BOOTP, say), and you then permanantly allocate that IP address to that machine, you would have permanently lost the address from the pool even if the machine is later taken out of your network.
DHCP introduces the concept to lease, whereby, the lease of the address needs to be renewed periodically, failing which, the address to returned to the pool.
As the machine has be configured to be assigned an IP address by DHCP, it requests for an address on each reboot. The DHCP server then knows that this IP address is definately in use, and reserves it on behalf of the machine for a furthur period of, in your case, 7 days.
Only if there is no request/renewal request for 7 days, the address is returned to pool.
The concept of T1 and T2 times are to ensure that: if the machine is kept continuously on for days, there will not be a situation that the machine is running but it's IP address lease has lapsed. So, T1 and T2 are kept at figures less that 100%, and also the reason that T2 > T1.
|
|
|
|
|
