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DHCP and auto-login System
My computer is on DSL behind a router that uses DHCP. The connection was dropped this morning and Mac OS X's DHCP did not log back and in and get the new information from the router. I had to change the Network preferences to BootP, close the panel, and then return and select DHCP again. OS X logged back in to the router.

Is there any way to make DHCP log back in automatically?
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that's odd
Authored by: Anonymous on Mar 29, '01 10:10:07AM

my cable modem uses DHCP, and i've been playing with a local network to put my new laser printer on - yesterday i cut the connection several times from the cable modem to the mac, and every time, OS X re-established the connection within seconds. i even checked the IP's, and they were different each time...


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DHCP Lease Renewal
Authored by: JohnDavidson on Jun 19, '01 11:19:35AM

I have a similar problem - I work in an enterprise that has DHCP servers all over the campus. When I go from one physical location to another, I'd like to put my PB/G4 running OSX to sleep, and wake it up in the new location and gain a new DHCP lease.

I've tried the script posted here which HUPs (resets) the UNIX network daemons, but that only works for me if I'm going to use a fixed IP address, not DHCP.

Does anyone know what the BSD networking commands are to force DHCP to drop/renew an IP lease?

Thanks in advance.


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DHCP Lease Renewal Problems
Authored by: JohnDavidson on Jul 06, '01 09:18:18AM

I fixed my DHCP problem, but boy do I feel foolish.

He's a word of warning to those having difficulty getting a DHCP IP lease renewals - be sure to check your network security firewall rules (if you use ipfw) and make sure that the ports needed by DHCP (67 and 68) are not blocked. I had tightened my firewall down so tight that I could no longer negotiate a DHCP lease once my initial lease (gained in the boot sequence before the firewall rules kicked in) expired.

Thanks to the very nice firewall utility Brickhouse ( I was able to review my firewall setup with "reasonable" settings that allow things like DHCP and NTP through, but still keep me pretty safe from most outsider threats.

Hope this helps someone.

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DHCP Lease Renewal
Authored by: octavio on Apr 02, '02 09:03:58PM

Did you find the BSD networking command to force DHCP to drop/renew an IP lease??
I just got a cable modem and still can not make the DHCP client on the OS X 10.1.3 box to successfully connect to the DHCP server at the ISP network.
It keeps on timing out and getting an invalid 169.x.x.x IP address instead.

However, if I manually configure a valid IP address (that I get when I connect my Win2000 PC to the cable modem instead), I can navigate for a while, until the valid IP address expires.

This is very weird, my Win2000 PC does not have any problem to get a valid IP address, but my OS X box simply can not connect to the DHCP server. Does anyone have any recommendation of the files/config params. that I should look at?

Thanks a lot.
- Octavio

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DHCP Lease Renewal
Authored by: JustyTylor on Apr 04, '02 03:43:25PM

Hmm. Sounds, for one thing, like the first poster wasn't noting a problem so much as how smoothly DHCP works for him. DHCP is *supposed* to give you a new address if you cut your cable modem connection, especially since there are so many people on that same system starting up/restarting/etc. their own computers. There would be quite a bit of IP shuffling.

Okay, so on to the other problems. At this point, the only thing I can really say is that I have never had a problem switching my PowerBook G4 667 from my work connection to a school connection in my office, or to my home connection, where I connect to via an AirPort basestation running DHCP to allow my Blue and White G3 to connect via ethernet (I share a DSL connection between the two of them). One thing I have occasionally done to make the transition easier between my different locations is to log out, put my computer to sleep, and log back in when I get to my destination. At the worst, I'll have to input my closed AirPort network's name and password to use my home LAN. So, the long-out/sleep/log-in steps might solve this problem without being as troublesome as shutting down and restarting.

My two cents,


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DHCP Lease Renewal
Authored by: tomdarch on May 10, '02 01:22:35AM
I'm getting similar problems with 169.x.x.x

I've got a DSL line running through an ethernet switch.

When I first hooked up my new powerbook it got a good address, but after disconnecting it then reconnecting it later, it hasn't yet been able to get a good address. When I only had os9 on my B&W G3 it had the same problem - I tried trashing the TCP/IP prefs, to no avail! Now that I've upgraded the B&W, it got a bad address the first time I tried connecting. I switched to PPP in the Network panel, hit "Apply Now", switched back to DHCP, hit "Apply Now", and it momentarily showed 0.0.X.X, then got a good address. Interestingly, when I get a bad (169.x.x.x) address, the subnet mask is set to and I don't get a router address.

Could this be a problem with the DHCP server? Is there a file to edit or trash in OS X that has DHCP settings or info? Does Apple's use of DHCP with AirPort have anything to do with this?

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DHCP Lease Renewal
Authored by: Myrddin on Jun 04, '03 11:26:45PM

I personally would like to know what the answer is... I don't shut my system down and would perfer to put it to sleep but getting a 169.x.x.x address instead of the proper router DNS address is a pain.

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DHCP Lease Renewal
Authored by: germsteel on Jul 05, '03 03:49:27AM

Check to see if you have set your router with enough IP addresses to hand out. Something that says starting IP address range to ending IP address.

My router hands me a new internal IP address and doesn't purge the old one for a little while.

Good luck.

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DHCP Lease Renewal
Authored by: anti-os on Nov 04, '04 05:58:46PM

Sounds like another case of an open transport issue. Funny thing if this was a "standard" wireless device (res. gateway) it wouldn't try pushing a 169.x.x.x ip first and wouldn't cause things to screw up. Just like OS10.x open transport problems.

Hmm... do I see a pattern forming here!


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