renewing the dynamic IP address

Hi

Sometimes I unplug the Ethernet cable momentarily, and plug it back in.
After I do that, the IP address is not always renewed. Usually it's not a
problem, unless I connected the PC back to a different network, and I must
get a new IP.
Question is - when does Windows renew its IP, and when doesn't it?
Can I configure something to have it always renew it's IP after plugging the
cable?

Thanks

Open a command prompt, type "ipconfig /renew" without the quotes.

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"David" <David@discussions.microsoft.com> wrote in message
news:616314B3-DEC8-4295-A988-BEB6D81B1970@microsoft.com...
> Hi
>
> Sometimes I unplug the Ethernet cable momentarily, and plug it back in.
> After I do that, the IP address is not always renewed. Usually it's not a
> problem, unless I connected the PC back to a different network, and I must
> get a new IP.
> Question is - when does Windows renew its IP, and when doesn't it?
> Can I configure something to have it always renew it's IP after plugging
> the
> cable?
>
> Thanks

=?Utf-8?B?RGF2aWQ=?= <David@discussions.microsoft.com> wrote in
news:616314B3-DEC8-4295-A988-BEB6D81B1970@microsoft.com:

> Hi
>
> Sometimes I unplug the Ethernet cable momentarily, and plug it
> back in. After I do that, the IP address is not always renewed.

How do you determine that the IP address is renewed? By looking at the
lease dates? By unplugging the cable, the DHCP server has no idea that
the machine is not still there and will maintain the IP address
reservation until it times out (sometimes days). When plugging the
machine back in, Windows will try to obtain an IP address from the
server, but the server has no idea that the computer was ever gone, so
it will simply inform it of what it thinks is its current address. The
lease date/time may not be updated.

Ideally, bring up a command prompt and type:
ipconfig /release
before disconnecting the cable. This will formally return the IP
address back to the DHCP server and force a DHCP cycle when reconnected
-- but don't be surprised when you get the same IP address you had
before.

> Usually it's not a problem, unless I connected the PC back to a
> different network, and I must get a new IP.

Obtaining an IP address *should* happen automatically when plugging
into different network.

> Question is - when does Windows renew its IP, and when doesn't it?

It _renews_ its IP when the lease is 1/2 over. It attempts to _obtain_
an IP address when senses a connection to a new network.

> Can I configure something to have it always renew it's IP after
> plugging the cable?

It should always try to obtain an IP address when connected. Unclear
is your definition of "renew".

-- John

"Dynamic" means exactly that - the address is assigned each time you connect
and will be different each time - it would be unusual to have the same
"dynamic" address assigned when unpluging and replugging - a "static"
address would not change.


"David" <David@discussions.microsoft.com> wrote in message
news:616314B3-DEC8-4295-A988-BEB6D81B1970@microsoft.com...
> Hi
>
> Sometimes I unplug the Ethernet cable momentarily, and plug it back in.
> After I do that, the IP address is not always renewed. Usually it's not a
> problem, unless I connected the PC back to a different network, and I must
> get a new IP.
> Question is - when does Windows renew its IP, and when doesn't it?
> Can I configure something to have it always renew it's IP after plugging
> the
> cable?
>
> Thanks

"AJR" <ajrjdr@comcast.net> wrote in
news:#gwQO7jAJHA.4992@TK2MSFTNGP06.phx.gbl:

> "Dynamic" means exactly that - the address is assigned each time
> you connect and will be different each time - it would be unusual
> to have the same "dynamic" address assigned when unpluging and
> replugging - a "static" address would not change.
>
>

On the contrary... DHCP has a strong preference to maintain the same
IP address when obtaining an address. Only if the "old" address were
no longer available or not valid on the current network would the
request be denied and a different address be assigned. When this
happens, a warning is logged in the System Events Log.

-- John

Hi
It really depends on the DHCP server.
Most End-Users have a Cable/DSL Router that includes a DHCP server and it
assigns the IP.
Some Routers would behave like the OP posted above, others might have
various behavior.
A Good Router includes a DHCP server that can Reserve an IP within the DHCP
range. I.e it remembers the MAC number of the computers and assigns the same
IP to the same computer.
Otherwise, if you need the same IP configure the computer with a static IP
that is out of the range of the DHCP Server.
Jack (MS, MVP-Networking)

"David" <David@discussions.microsoft.com> wrote in message
news:616314B3-DEC8-4295-A988-BEB6D81B1970@microsoft.com...
> Hi
>
> Sometimes I unplug the Ethernet cable momentarily, and plug it back in.
> After I do that, the IP address is not always renewed. Usually it's not a
> problem, unless I connected the PC back to a different network, and I must
> get a new IP.
> Question is - when does Windows renew its IP, and when doesn't it?
> Can I configure something to have it always renew it's IP after plugging
> the
> cable?
>
> Thanks

Thanks for all the replies, guys,
but I was looking for something else.

Using release/renew is what I do now, but want to avoid it. Many times I
(and others at the office) forget it, and end up using a wrong IP on a
different network (may cause collisions some times).
By "renewing the IP" I mean - sending a DHCP-REQUEST to the DHCP server, and
either keep its IP if it gets an ACK, or start a DHCP-DISCOVER session to
obtain a new one if it gets a NACK.
Of course, if the PC stayed on the same network, the DHCP server will reply
with an ACK to the PC's request, so it will maintain the same IP; but if we
change to another network, we will get a NACK and start a DHCP-DISCOVER
session to receive a new IP.
You can see if the IP was renewed by the obtain time in "ipconfig /all", and
I even used Wireshark sniffer - and I see that sometimes the PC sends a
DHCP-REQUEST after plugging the cable back in, and sometimes not.

Appreciate your help.