Self Assigned IP / DHCP problem : sharing my fix.

Okay. I WAS frustrated for a long two weeks before I figure this out. It seems that this problem has affected a LOT of people out there, and since I now am (supposedly) free of this thing, I want to share my hypothesis of the problem's roots (A) and my fix (B).
Note that:
- i'm free of this problem since the last one week, so .. well, hopefully this is right.
- the problem happens almost anywhere, with any router types, and in any connection type, be it ethernet or wireless a/b/g/n.
- the problem is automagically fixed by running into safe mode.
- the problem keeps happening again and again, although you have powercycled everything of the electronic peripherals in your house, even by disconnecting your phone/ADSL line and main power fuse.
- disabling the Mac OS X Application Firewall sometimes cures it, but most of the time it happens again.
- AFAIK (correct me if i'm wrong), the ipfw, mother of all OS firewall, exists within Mac OS X, and the Mac OS X Application Firewall (i call this OSXAF) has nothing to do with ipfw.
A. My hypothesis and the reasons.
* for an unknown reason, there is a rule created for ipfw that tells it to block the ports 67 and 68, both are the common DHCP ports.
* because of that, your Mac cannot contact with any DHCP servers, anywhere. This forces your mac to assign an IP address by itself.
* disabling OSXAF incidentally removes that rule, but after (one or a few times) reconnect or reboot, the rule appears again.
* powercycling your routers or anything related does not concern ipfw, thus has no effect whatsoever to the problem.
B. My fix.
1. Get the WaterRoof free ipfw frontend (forgot the site, just google)
2. Open it.
3. Go to Static Rules part.
4. Find everything which reads "deny blah blah blah port blah,blah,67,68,blah blah"
5. Edit those rules so that there is no 67 and 68 inside.
6. Open tools -> rules configuration -> save to startup configuration -> yes.
7. Open tools -> startup script -> install startup script -> yes.
That's all.
For me, this seems to be a permanent fix. Please note that the startup script mentioned before exists in all *nix-based machines, so don't worry about startup time, there'll be no slowdowns (again, please correct me if i'm wrong, i had only little experience with *nixes). Besides, i suspect that if you don't save and reinstall that script, the previous script is the one which has 67 and 68 inside.
Hopefully this helps. Any corrections, comments, suggestions, and/or knowledge are welcome.
Cheers,
-bam, the noob.

OK, so a little background -
I have an MBP with 10.5.5 (which I downloaded yesterday, so that's not the issue). This year at school they upgraded the wireless system and network control to Foundry routers and Bradford Securities Network Control. Problem is, my computer is intermittently and randomly having a hard time sticking with one IP and staying away from a self-assigned 169 IP. The System Prefs are fine, and even when I change to manual settings for the IP, it doesn't stick. I checked the terminal (tcpdump) and it seemed to be having a tough time accepting one of the two IPs the servers offered (there are two servers for redundancy). It asked for an IP, gets two offers, and then asks again. I was stumped, and so were the IT guys on campus. And it's not just me, many other 10.5 users are having the issue. And it's not the network, because nobody else is having the issue but 10.5 users. Certificate problems are similarly eliminated from possibility.
The IT guy showed my this thread, and I was excited, so I first tried to just shut off the Firewall all together, and that worked, briefly, but now it doesn't matter if the Firewall is on or off, the problem persists. I tried your WaterRoof method, and the similar program NoobProof, but there were no rules relating to ports 67 or 68 at all, let alone denying them. (As a side note, when my FW is off, there's only the rule allowing all IPs in and out, and when it's on (but only allowing specific programs) it gives a second rule that denies "icmp from any to me in imcptypes 8." No idea what that means.) I've been watching tcpdump and the FW logs closely (as well as the console itself), but nothing has changed. The only interesting thing is that when the IP changes from the (good) 137 IP I'm supposed to have to the (bad) 169 IP, often times (in fact, most times) there is no firewall activity. The console says that the en1 link (wireless) is now down, and the tcpdump picks up the computer asking for an IP again, but the firewall logs pick up nothing, neither through the console or through WaterRoof. Which is weird, because I thought it was a FW problem (as did the IT guys), but the logs show that only occasionally when the servers offer me an IP does the FW block the request, but not all the time.
As another point to note, this is not only an issue with the wireless. The wired connection (Ethernet right into the wall, and attempted from many different plug-in sites) also has this issue.
My only conclusion is that the FW is buggy, or that the logs are missing denials, neither of which makes much sense, IMHO.
Any thoughts?
EDIT: Shutting off the FW often solves the problem, but not always. Sometimes I can get a correct IP even with the FW in full swing without anything popping up in the logs. And sometimes I can't.
Message was edited by: kangasaurus

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    macbook pro   Mac OS X (10.4.6)   mac mini
    macbook pro   Mac OS X (10.4.6)   mac mini
    macbook pro   Mac OS X (10.4.6)   mac mini
    macbook pro   Mac OS X (10.4.6)   mac mini

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