Ok. I have 3 computers connected to my Linksys BEFSR41 Router which is currently running 1.42.6 Firmware.  
 
Now 1 of the computers runs my FTP Server. Another computer I use for IRC so I need it to be able to DCC send/receive files.
 
In the DHCP Clients Table it would label any given computer either 192.168.1.100, 192.168.1.101, or 192.168.1.102. Depending on when the computers were shut off and on, the IP would change for any given computer. So sometimes the FTP Server would be 192.168.1.100...the next day it might be .101.
 
Now I obviously went into Port Forwarding & forwarded Port 21 to ALL of the 3 possible IP addresses (.100 to .102). I did the same for the IRC DCC port range.  
 
However today my FTP Server was not accessible for some stupid reason. I found out it was because my FTP Server's IP changed and in the Port Forwarding section the computer was in the middle of the list. Once I swapped it's IP address to the top of the list it worked just fine!
 
This NEVER happened before. Where I put the IP's on the Port Forwarding list never used to matter.
 
Currently I found how to setup a Static IP in Windows XP from some website & did that to the FTP Server. Problem is, when my Cable Modem service changes their DNS numbers I'm screwed until I change them manually.
 
What I'm guessing is that the DNS change at my ISP will happen a lot less often than my internal network changing the local IP numbers (which would cause me to keep manually bumping the FTP Server's Local IP number to the top of the Port Forwarding list).  
 
Here's a funny sidenote that's baffling me. On my 2nd computer....the one that needs access to DCC in IRC....I found that DCC sending & receiving will function NO MATTER WHERE I put the lousy computer's Local IP number in the Port Forwarding list!!! Go figure.
 
Does anyone have a permanent solution for this? The ONLY thing I can think of is that the newer firmware is causing this.
 
Would going to an older version fix things? Am I overlooking something?  
 
Thanks for any help you can give.

What exactly does this mean?  Does your cable company have an entry for you?  If so, that would refer to your Lilnksys wan port, not any PC's behind it.  Can you clarify?
 
<i>It's always the one thing you never suspected.</i>

On your LAN - Assign specific static IP's to special functions...
Like assign 192.168.1.11 to the FTP server box - then forward same...

Sure thing. Linksys's Knowledge Base mentioned to create a Static IP in Windows XP in order to setup an FTP Server. I found this website that had better instructions than Linksys (http://linksysftp.dyndns.org/).
 
I also found a review on ArsTechnica of the router that mentioned the problem with setting up a Static IP (like the one I just mentioned) is that if the DNS numbers change, I would have to change them manually in Windows XP in order for people to maintain access.  
 
Unlike doing everything with DHCP in the router....where the router would automatically keep everything in order.
 
Hence my problem...
 
In the router's web interface I must keep the FTP Server at the top entry in the Port Forwarding list, otherwise it won't let anyone connect. So I figured the possibility of the cable company changing the DNS numbers was less than the local IP changing in DHCP...so I setup the Static IP as a temporary fix.
 
I just want to have it so I don't have to worry about the FTP Server possibly going down at all.

 
Sorry if I wasn't clear...please check my 2nd explanation above.....I did do what you suggested. My concern....which was brought about in that ArsTechnica review of the router....is the Cable Company changing DNS numbers. Because then I will have to manually change the Static IP setting in Windows XP to keep the server running.
 
I want to find a solution so the server will always run no matter what.

I'm still confused.  Your WAN IP address on the router is the one the Cable company gives you.  That is a dynamic address (DHCP) so it is just as likely to be switched on you as the ones you were serving out to your PC's on your LAN.  
 
DNS relationship:  Does the cable company actually give you a name along with an address?  If so, that name will be linked to whatever address you have leased from their DHCP server at the time, which of course is under the same dynamic lease rules as your IP address.
 
Now, (I can't determine this from your posts) if the Cable company is giving you a STATIC IP adress, the 2 paragraphs above are irrelevant.  In that case, the Cable company's DNS server should not be changing your name, if they are it is a problem you should take up with their support people.
 
<i>It's always the one thing you never suspected.</i>

Ok...here's the exact portion of the ArsTechnica review that has me concerned...
 
<<The only real problem with using static IP-addresses is that you must manually assign each of your devices on the LAN a unique IP-address, as well as entering in the default-gateway and DNS information on each device.  If your ISP ever changes their DNS addresses, you can't update them in a single location (in the Linksys router) and have that propagate to each of your LAN-connected devices.>>
 
Now my Cable Company does not give me a Static IP. It's dynamic. I know that changes on a semi-regular basis, but does the DNS addresses change as frequently? This is the part i'm unfamiliar with. I'm only assuming the DNS addresses will change less frequently than my internal IP's will in my router's DHCP Client Table.
 
Now back to my original problem. If the DNS addresses change. I will have to change them manually in the TCP/IP settings in Windows XP to keep the server alive.  
 
I don't want to do this. I want a solution that will have it always on no matter what changes.
 
I *used* to enjoy this by not setting up a Static IP in Windows & letting all the machines be controlled by the router's DHCP. Then just port forward 21 on all 3 IPs the router would use. But now my router wants the IP for the FTP server on the top of the list only. No idea why. I used to be able to put it anywhere in the list.  
 
So hopefully now I made my problem even more clear (hopefully ). If I go the Static IP route...the DNS addresses could change, killing the server till I manually update it. If I go the DHCP/Router route...then once my FTP Server's internal IP changes, it will kill my server until I can manually push the new server address to the top of the Port Forwarding list.
 
What my hunch was, was that my updating of the Firmware somehow created this little fluke in the router's DHCP/Port Forwarding feature. I was hoping for confirmation from someone else with a Linksys router.

Nope - the address of THEIR DNS server will pretty much never change.  Not something you should worry about.
 
<i>It's always the one thing you never suspected.</i>

you should read up on port triggering.  you can set the router up to forward the needed ports to what ever computer starts up a server.
 
how do you shoot the devil in the back?  what happens if you miss? -verbal

Thanks. I see the button for Port Triggering in the Port Forwarding section of the web interface...but honestly don't know how it works. I will read up on the manual to see.

Very Cool! That means the Static IP solution is pretty much a permanent fix.

I'm looking at your original post, and wondering about something:
 
Is the whole reason for this exercise trying to run an FTP server with a static IP address?  If so, that will never happen reliably unless you pay extra for a static IP address from your ISP.  You can give your internal nodes all static addresses, and the ISP's DNS server address will never change, but your WAN IP address is still dynamic no matter what you do.  So people trying to access your FTP server will always have to know what the current address is, as there is no guarantee it will remain static.
 
That being said, I seem to remember tricks to somehow periodically send out your current WAN IP address to some Internet site somewhere, which would allow outsiders to always know the current address of your server.  If I run across something like that I'll be sure to post it.
 
If my whole premise is wrong, let me know why you are setting up your internal nodes statically.
 
 
 
<i>It's always the one thing you never suspected.</i>

jlanka...
 
"I seem to remember tricks to somehow periodically send out your current WAN IP address to some Internet site somewhere, which would allow outsiders to always know the current address of your server. If I run across something like that I'll be sure to post it."
 
*** I'd sure like to know that trick!  
My BellSouth DSL connection with LinkSys router, set MaxIdleTime=0 and KeepAlive, keeps the same WAN Ip for quite a long time - but does change occasionally(powerout or BellSouth knockoff). If I'm not home, and can't get thru I have to call a neighbor to go over and get my current Wan IP for me - a bit of a pain.... Being able to sent the current Wan IP somewhere would be great!!!
 
The Dynamic Wan IP is so much of a problem I've considered gonin with Direct DSL just to get a Static IP.... (and DirectDsl is 10 bucks cheaper per month - $120 per year)
 
It would be pretty easy to send yourself an Email with MAPI(MailAPI) if ya could get to your WAN IP easily... The only way I know to get your Wan IP is with the LinkSys "Status" page - and that would be a non-trivial tast to get to programaticly. Knowing how to get that Wan IP and sending to somewhere would really be a nice trick!!!

I think a guy I work with (who isn't in yet - the lazy bum   ) knows about this.  I'll post as soon as he gets in.
 
<i>It's always the one thing you never suspected.</i>

Ok, no this is not the issue. I apologize if my half-assed grasp of the situation is causing confusion. When people connect to my FTP they use a dyndns.org address. I run a little proggie on my system that periodically updates my dyndns.org name to the current address my cable company gives me. So that parts ok. It's the router that's the problem.
 
My router randomly gives each of my 3 computers an internal IP via DHCP. So at any given time my FTP server could have an internal IP of 198.162.1.100/.101/or .102.
 
So in the Port Forwarding section I forwarded port 21 to each of these internal IPs. That way I'm covered no matter what the router assigns to my FTP computer.
 
Now the problem happened this weekend when no one was able to access my FTP server. I found out that in the Port Forwarding table, in the router's web interface, my FTP server's internal IP MUST be placed at the TOP of the list.  
 
This never happened before and you can hopefully see the dilema. ie: If I put "Port 21 - 192.168.1.100" at the top of the list and then my FTP server changes to 192.168.1.101, I'm [-peep-] & have to change the top entry in the Port Forwarding table to the current internal IP of the FTP server. Again, something that should NOT be happening, but is.
 
So I read online that I should setup a static IP address internally in Windows on the FTP computer. So I went into my local settings and setup a static IP for that specific machine to 192.168.1.2. And I forwarded port 21 for that new internal IP in the router's interface.  
 
It still needs to be at the top of the Port Forwarding list for some ungodly reason, BUT since it's internally static, the router's changing of things via DHCP should not affect things.
 
And I thought I had it all fixed last night...FTP server was working with no problem (I had the FTP server software ON at the time I created the Static IP).
 
However I shut the Server software down & when I went to restart it this morning, the [-peep-] software (Serv-U) won't start now. I was late for work & couldn't screw with it, but that's where I am right now.

OK - I see what you want now.  You should basically be in business.
 
BTW - that dynadns.org stuff is what compsci is looking for.
 
<i>It's always the one thing you never suspected.</i>

 
Yeah, provided I can figure out why my stupid Serv-U software won't turn on now. Problem with accessing 127.0.0.1 was the type of error I got this morning. I'll have to fiddle with that when I get home tonight.
 
Glad I could help someone. Dyndns.org is pretty cool & I've been using it for a while.