When do IPs change?

  • Thread starter Thread starter Jim Slager
  • Start date Start date
J

Jim Slager

Under DHCP wireless when do IPs get assigned to
computers? Is it only when they boot up or can it occur
at any time. If I change, say, the Starting IP address
will the router go out and start reconfiguring the network
immediately or will it wait until each computer is next
booted?
Or if I enable static IP will this take effect immediately
or when computers boot?
 
With Dynamic Host Configuration Protocol (DHCP), IP addresses are "leased"
to the clients. These "leases" are for a set period of time and have to be
renewed at the end of the time period. The protocol provides mechanisms for
obtaining & renewing the leases.

On some routers you can configure the "lease period". You can go in and
change it - say - from 2 days to 2 weeks. On other routers it's
preconfigured & unchangeable. In a typical household network - with 2 or 3
computers - a long lease period works fine. But in an office network with
many users coming & going they will typically have a much shorter lease
period - so they can recover & recycle abandoned IP addresses.

Typically, the DHCP server will just go ahead and extend the lease for a
client requesting a renewal - i.e. the IP address does not change. This is
a function of however of how much contention there is for IP addresses.

If you have a client PC that you don't use very often - e.g. once every 3 or
4 days - and the lease period is 2 days, you may find that it winds up with
a different IP address every once in a while.

If you have Windows 95/98/ME you can view the lease time by running a
program called WINIPCFG. It will tell you when the lease was obtained and
how much time is left. If you have Windows 2000/XP, you can view this
information in a DOS window. Type "IPCONFIG /ALL".

To answer your other questions:

With regard to changing the starting IP address - NO, the router will not go
"OUT" and reconfigure the network. It doesn't work that way at all. DHCP
is a passive mechanism that's initiated by the clients & RESPONDED to by the
server. It does not reach out with tentacles & manipulate its clients...

If you assign static IP addresses to your clients, this does take effect
immediately, but you *may* have to reboot after making this change. If you
DO assign static IP addresses, you must assign them from OUTSIDE your
dynamic address pool. Typically you'll have a set of addresses available
like 192.168.x.1 through 192.168.x.254. Check your documentation / go into
the router config to find out which of these are in the pool. If you assign
a static address that's in the DHCP pool, you'll run the risk of getting an
IP address conflict (two machines fighting over the same address).
 
Thanks, Melvin. You are a tremendous help. If I want to
change my wifi network from dynamic to static how about if
I change each wireless computer first and then shut it
down. Then change the router and boot the computers.

The only thing I'm worried about is the computer I'm using
to program the router. What if I lose connection to it
immediately upon saving settings? Does it help that the
computer I'll use to program the router is a "wired"
computer?
 
Back
Top