Newbie DHCP question

I'm not sure I fully understand the principle behind DHCP. This is my
scenario/configuration.

I've got a small home network using a Linksys router (WRT54G) and have
my main computer connected directly into the router. Until recently, I
had the router default settings for DHCP (I had changed everything
else) but was trying the port forwarding option for some gaming. In
doing so, I was under the impression (after reading information on port
forwarding) that I had to change my setup to a static IP, so I did.

After fooling around a bit, trying different settings, and talking with
a tech at my local university, I realized that I didn't have to have a
static IP, but rather extend the "refresh time" (is that the correct
terminology?) for my DHCP. I did this and everything ran smoothly.

Curiosity (evil thing) being what it is, I decided to check my IP
address using ipconfig /all and discovered that while it did show I had
DHCP set up (complete with lease expiration times) it was still the
same original IP from the day prior. So, to verify, I shortened the
lease time in my router's settings to one minute. I wanted to see two
things: first, if it was actually changing my IP; and second, if the
change would affect my connection. So after shortening the time, I ran
WMP and streamed my local NPR, all the while checking with ipconfig
/all if anything was changing.

Two things I noticed were that neither the IP address was changing -
the lease expirations did change every minute - nor was I experiencing
any significant interruptions in the streaming radio. Perhaps gaming
would be different, though, and I might test that later.

Sorry this is so long-winded; perhaps my questions are even mute,
because I don't seem to have a full grasp of how DHCP works. Am I NOT
supposed to get a "new" IP with every lease expiration? Will there be
a significant interruption in my connection?

Thanks for your time and feedback,
Andrew

On 16 Feb 2005 10:49:19 -0800, (E-Mail Removed) wrote:

>I'm not sure I fully understand the principle behind DHCP. This is my
>scenario/configuration.
[snipped]

So you set the lease expiration down to 10 seconds.
At 5 seconds the nic will attempt to dhcp renew the *existing lease*.
If it succeeds, no change to the assigned ip address occurs - and your
expiration goes back up to 10 seconds.

Repeat as necessary...

If you are constructing "interesting" application port forwards, it's almost
always easiest to do so with static addresses for the target node(s).
Systems that are not port forward targets can continue using dhcp without
issue...

Cheers

/daytripper

daytripper wrote:
[edit]
> If you are constructing "interesting" application port forwards, it's
almost
> always easiest to do so with static addresses for the target node(s).

> Systems that are not port forward targets can continue using dhcp
without
> issue...
[edit]

So if there are only 2 (two) systems on the network, and we're both on
for extended periods of time, then in practice, port forwarding with
DHCP shouldn't be an issue. And if it becomes one, because of a
changed IP address (for example my wife logs on before I do) then I
just need to change the IP address the port is forwarding to, correct?

Thanks!
Andrew

(E-Mail Removed) wrote:
> daytripper wrote:
> [edit]
>
>>If you are constructing "interesting" application port forwards, it's
>
> almost
>
>>always easiest to do so with static addresses for the target node(s).
>
>
>>Systems that are not port forward targets can continue using dhcp
>
> without
>
>>issue...
>
> [edit]
>
> So if there are only 2 (two) systems on the network, and we're both on
> for extended periods of time, then in practice, port forwarding with
> DHCP shouldn't be an issue. And if it becomes one, because of a
> changed IP address (for example my wife logs on before I do) then I
> just need to change the IP address the port is forwarding to, correct?
>
> Thanks!
> Andrew
>
Right. But with only 2 systems, there's probably no reason to use DHCP
in the first place. Static IPs should be easily manageable.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

(E-Mail Removed) wrote:
> Two things I noticed were that neither the IP address was changing -
> the lease expirations did change every minute - nor was I experiencing
> any significant interruptions in the streaming radio. Perhaps gaming
> would be different, though, and I might test that later.
>
> Sorry this is so long-winded; perhaps my questions are even mute,
> because I don't seem to have a full grasp of how DHCP works. Am I NOT
> supposed to get a "new" IP with every lease expiration? Will there be
> a significant interruption in my connection?

The "Dynamic" in DHCP (Dynamic Host Configuration Protocol) is not as
dynamic as you think. This dynamic doesn't necessarily mean "ever
changing", it just means "able to adapt".

Once it's booted a PC with a certain set of values, it will remember the
PC's MAC address and store it in its own ARP cache. So next time the PC
gets booted, all it needs to do is refer back to its ARP cache and
reassign the same IP and other information to it again.

It's conceivable that you can get another computer, boot it up on the
network before your own computer and you will find that it takes over
what used to be your computer's IP address before. Then when you boot up
your own computer, you'll find that it doesn't just wait there waiting
for the other computer to give back its IP address. Instead the DHCP
will just assign it a new IP address.

Yousuf Khan

most routers will only give new IP addresses if you turn your system off and
waite for the lease to expire then turn on your system. The router should
give a new IP then.

Robert...

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> I'm not sure I fully understand the principle behind DHCP. This is my
> scenario/configuration.
>
> I've got a small home network using a Linksys router (WRT54G) and have
> my main computer connected directly into the router. Until recently, I
> had the router default settings for DHCP (I had changed everything
> else) but was trying the port forwarding option for some gaming. In
> doing so, I was under the impression (after reading information on port
> forwarding) that I had to change my setup to a static IP, so I did.
>
> After fooling around a bit, trying different settings, and talking with
> a tech at my local university, I realized that I didn't have to have a
> static IP, but rather extend the "refresh time" (is that the correct
> terminology?) for my DHCP. I did this and everything ran smoothly.
>
> Curiosity (evil thing) being what it is, I decided to check my IP
> address using ipconfig /all and discovered that while it did show I had
> DHCP set up (complete with lease expiration times) it was still the
> same original IP from the day prior. So, to verify, I shortened the
> lease time in my router's settings to one minute. I wanted to see two
> things: first, if it was actually changing my IP; and second, if the
> change would affect my connection. So after shortening the time, I ran
> WMP and streamed my local NPR, all the while checking with ipconfig
> /all if anything was changing.
>
> Two things I noticed were that neither the IP address was changing -
> the lease expirations did change every minute - nor was I experiencing
> any significant interruptions in the streaming radio. Perhaps gaming
> would be different, though, and I might test that later.
>
> Sorry this is so long-winded; perhaps my questions are even mute,
> because I don't seem to have a full grasp of how DHCP works. Am I NOT
> supposed to get a "new" IP with every lease expiration? Will there be
> a significant interruption in my connection?
>
> Thanks for your time and feedback,
> Andrew
>