Fixed or dynamic?

The Astroman

The Astroman

Active Member
Hey guys!
I set up my D-Link DG834B modem/router so that devices on my network always get the same IP (I think it relies on the MAC address of the device). Weirdly however, the devices sometimes show up with different IPs...

1) Does my router actually just reserve a particular IP for a particular device (so that no other MAC address than the device's can have that IP), not actually forcing it to have that IP (meaning it could have an other (non reserved) IP)?
2) If the answer to 1) is yes, I'm guessing I should setup the devices to a specific IP address (i.e. not "Obtain an IP address automatically", but "Use the following IP address").
 
This is the basic and non technical run down of how DHCP works.

DHCP = Dynamic Host Configuration Protocol

DHCP hands out IP addresses to your client machines on your network. Each IP must be unique to each client on your network. Basically the DHCP server sits there and just broadcasts out the fact that it can give an IP. It is saying, hey you need an IP? Then the client machine when it hits the network it is going to call out for an IP. So the client says, hey I need an IP and the DHCP server says here you go little buddy. Then the server has what is called a lease time. The lease time is how long the IP is allowed out to that client. So, if the lease time were say, 1 hour after that 1 hour was up the DHCP server would say hey, you still using that IP, because if you are done I can give it to someone else.

If you are still on the network the client will say yeah dude, I am still using it bugger off. So the DHCP server will renew that same IP back to that same client for another full length of lease time.

Also, typical behavior of a DHCP client is that it will request the last IP it had. So, if you leave from network A to Network B across town on your laptop and connect to the new DHCP server your client will say, hey last time I had an IP I had 192.168.1.150, can I have that number again? If it is available the server will give it that IP and if it is not the sever will say no, but here is a different IP for you.

So, yes by default the client will request the same IP over and over again and if that IP is available the server will oblige and give them that IP. If that IP is not available for whatever reason they will get a new one.

Now if you want your DHCP server to give the same IP to a particular client over and over again you can set up what is called static DHCP, which is a lease of an IP assigned to the MAC address of that client's NIC. Most routers support this feature.
 
Thank you for your humourous and straightforward explanation of DHCP.
However, I'm still not sure whether or not I should set devices on my LAN to automatically acquire an IP, or set it to acquire a precise, fixed IP.
 
The Astroman said:
Thank you for your humourous and straightforward explanation of DHCP.
However, I'm still not sure whether or not I should set devices on my LAN to automatically acquire an IP, or set it to acquire a precise, fixed IP.
Click to expand...

The only time you ever need to run static IPs is that if you need to forward ports to a specific client from your router. Like if you were tunneling VPN or ssh to one of your machines from the interwebs to a specific computer on your network then you would need static IPs.

What are you trying to accomplish? What are you trying to run? Things like IP printers should have static IPs that way you print to the same IP over and over again. I run static DHCP on my desktops because I have torrent client running, remote desktop being forwarded to one machine, and I have my xbox 360 in a DMZ.
 
I'm running an FTP server and I have a multimedia server too (2 separate machines), I have gotten into the habit of giving each device their own IP, so how do I make sure they always have the same IP?

It's weird cause sometimes I can't find them... running \\DEVICE_NAME doesn't help either... any general things to check when this sort of problem occures?

Also, what difference does it make if the devices aren't in the same domain (workgroup)?
 
The Astroman said:
I'm running an FTP server and I have a multimedia server too (2 separate machines), I have gotten into the habit of giving each device their own IP, so how do I make sure they always have the same IP?

It's weird cause sometimes I can't find them... running \\DEVICE_NAME doesn't help either... any general things to check when this sort of problem occures?

Also, what difference does it make if the devices aren't in the same domain (workgroup)?
Click to expand...

Yeah you need to set up what is called DNS....that is a whole other situation.

If you router allows you to reserve IPs by MAC address then I would do so for each machine. Then I would look at installing something like dyndns.org or something similar to keep track of your DNS and IPs.

I would ultimately suggest you just pay for hosting. It is only $9 a month to host my site and I get unlimited everything
 
lol I'm not THAT nooby

I used dyndns a lot before...

however these servers are internal, i.e. are only used by local users.
 
The Astroman said:
lol I'm not THAT nooby

I used dyndns a lot before...

however these servers are internal, i.e. are only used by local users.
Click to expand...

if they are only used by internal clients you still need static IPs, which can be assigned via your router control panel
 
Maybe I wasn't clear enough, that is what I'm trying to do in the first place.

e.g.

Device "Computer A" always gets 192.168.1.2
Device "FTP Server A" always gets 192.168.1.3
Device "Computer B" always gets 192.168.1.4
etc.
 
It's already been said but you may have missed it in all the other stuff.
I run static DHCP
Click to expand...
That's likely what you want. If your router doesn't support it you can either get new firmware or you could use static IPs but that's a bit more configuration on the client side.
 
very good, i liked it. thankyou
i would like to change to a static. i wanted to access the computer and the ip changed. had to call the wife at home and get the ip to use. then again if i try this and start playing my wife will have a fit if her sheet does not work. we have 4 computers in the house. i will try and read this many time before i play.

enjoyed it tlarkin........thanks
 
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