IP Addresses flip-flop

[pendragon]

Every once in awhile, I notice that the IP address in my 2 networked (wired router) computers (both 10.4.9) trade numbers. This causes no problems of which I am aware, but it is a puzzlement.

What am I doing to cause this, and is there a way to intentionally reset them to their original state?

[bobw]

If you shut down the machines, then boot again, the IP numbers can change this way.

You can set the router to MAC address for each machine to the specific IP number.

[pendragon]

Thanks Bob,

I know the address change somehow relates to restarts, but I haven't a clue what's causing or directing this activity. Changing the startup sequence of the two computers has no apparent affect (as has changing the ethernet router ports).

Other than assigning my own IP addresses, have I no recourse?

BTW, are those IP addresses generated/assigned by my router or my computer(s)?

Ah, networking, another area in which I excel.

[kelly]

Usually it's your Router Harv.

DHCP.

"Most home routers and firewalls are configured in the factory to be DHCP servers for a home network. An alternative to a home router is to use a computer as a DHCP server. ISPs generally use DHCP to assign clients individual IP addresses."

http://en.wikipedia.org/wiki/DHCP

It will assign Private Addresses.

Is this a problem?

[pendragon]

I'm having no problems Sir Kelly. It's just that I am curious why (and how) sometimes it's one way, and other times it's the other. I know that the change occurs after some, but not all, shutdowns and restarts.

The issue (for me) is why it does what it does, and other than assigning a fixed IP address, do I have any control over the flip-flop?

[Xairbusdriver]

I have written about this unneccessary swapping before and have always been told, "It ain't no problem, get used to it!" However, if you use aliases of your other computer(s) on your Desktop for extremely simple drag-n-drop file tranfers or double-click access to said machines, it is a problem. Contrary to the ability of aliases in the file system to keep up with the directory location of the parent file location, a network alias cannot do this. So, when a machine or router is shutdown or suffers a power loss, the machines may get new IP addresses and the aliases are useless. Of course, one can always go through the "Go" menu and re-establish/recreate the aliases. No 'problem'.

But I grew tired of that and thought there must be a simpler, Apple way of setting up the LAN. There is, and it's Apple simple and stable.

Just assign the IP numbers you want to use to each machine and set the Network->Built-in Ethernet-TCP/IP "Configure IPv4:" to "Manual". You may have to ask you ISP for the DNS Server addresses, if they don't show up automatically. With a wired LAN your address will probably start with 192. With a wirless LAN the numbers usually start with 10. In either case, it's more helpfull to have each machine assigned consecutive addresses so the router can easily add new devices with numbers you'll probably know yourself. Don't start with x.y.z.0, start with ...1 and continue with as many machines as you have.

It doesn't even matter if your router still uses DHCP to assign addresses. It will simply and logically see that there are certain numbers already in use and use any of the remaining 250+ available.

And, all your aliases, will remai useable for file transfers! Regardless of what hapens to startup sequence/power stoppage/moon phases/'no problem' suggestions.

Would you carry a dozen keys for your car because you never knew which one would be required to start it next time? :headbash: But it's your LAN, create it any way you want.

[pendragon]

ABD,


As I am having no problems, well, besides being too dense to divine the rationale behind all this, I’ll not go the “manual” route. Art least not for now.

Perhaps if I have some time next week, I’ll try shutting down my entire system (computers, modem, & router) and see if I can force a change. Ah, the drama of it all.

[pendragon]

Problem/riddle solved (I think).

I know that IP addresses are normally assigned by the router, with the first number going to the first machine booting up and so on.

Even though I tried shutting down and rebooting in a different sequence, there was no change in the assigned IP addresses.  

Then it finally dawned on me.

My DHCP lease was for seven days. So I changed the lease to one hour, shut everything down (computers, modem & router) over night and then brought the system back up. Voila, I now know how the flip-flop occurs and what I can do about it.  

But other than being a tad bit smarter re routers, there is no operational benefit, at least in my case.

Can a little bit of knowledge be a dangerous thing? Nah, not for a TSer.

[Xairbusdriver]

The only DCHP lease time I'd use would be "Infinity"! Why bother with any changes? It's your LAN. Make it work for you instead of how someone thinks it should or how they did historically.

I think the confusion ( at least in my early learning and use ) comes from the fact that cable/DSL modems force us to use DHCP for connecting to the internet, just so they can provide a 'benefit' for the extra charge they ask for to assign you a permanent address. But that use of DHCP does not mean you have to use it on your own LAN.

OK, having a fixed IP address on the internet also gives you the advantage of running a web site on your local machine. And that's the reason the companies say you can't do it without paying extra. At least with a cable system, the speeds decrease every time another neighborhood machine on the accesses the internet. DSL may not have this problem, but I'll bet they still want to charge you for a 'static' address.