Probably nothing special would happen. Your machine would simply update the same IP address as before without you noticing a thing.
But example in my case, my IP webcam stopped working properly. My ISP leased a IP for 3 hours at time and as result my camera worked 3 hours and then jammed. No idea why this D-link DCS-5300W can=B4t update the leased IP, but works just fine with NAT.
As for your log question, I suggest you try it and report back :)
Dumb idea. No benifit. If you're running an open access point, with no encryption, every passing laptop will grab an IP address, and hold it forever. Eventually, you'll run out of IP addresses. This is exactly what happens at many coffee shop hot spots that use too long a lease time. If you're running a close and encrypted system, you're unlikely to have this problem.
Nothing. The Windoze algorithm for renewing the lease is to request a renewal at half the lease time. So, if you issue a 1 hr lease, Windoze will request a renewal after 30 mins. If it doesn't get it, it will pound on the DHCP server roughly every 12 minutes until it expires.
I don't think you can set it to 1/2 hour. Most cheapo routers have 1 hour as the minimum. Since you didn't bother disclosing what router make and model you own, I can verify if this is true for your device.
So, what problem are you trying to solve? If you just want to retain a MAC address to IP address mapping, just use the "static DHCP" feature found in many routers. In effect, it's an infinitely long lease time that doesn't screw up badly if the power is cycled and the leases are lost.
Renewal at 50% of lease time is standard for all DHCP clients.
Drivel: Where it gets really long is the Windoze WINS (NETBIOS to IP) renewal and extinction interval. The default times are: Renewal interval: 144 hrs (6 days) Extinction interval: 144 hrs Extinction timeout: 144 hrs Verify interval: 576 hrs (24 days) However, that's not the problem here.
For DHCP it's the clients responsibility to initiate renewals and the servers responsibility to know when to expire the lease. This article discusses how it works, and makes specific recommendations against ultra long DHCP lease time:
if the DHCP server goes offline for some reason, when the clients notice that 7/8th of the lease time has arrived without a renewal acknowledgment, they start spewing multiple DHCP discover messages (rebinding) trying to find another DHCP server. It probably won't generate any noticeable increase in traffic on a small network, but it's really ugly when it happens at a large ISP.
More detail on DHCP (3 pages): |
If you want to play, try this free DHCP query tool: |
Well, then shorten the router DHCP lease time to the minimum, which usually 1 hour. If the client disappears, it will disappear from the list within 90 minutes. Is that short enough? If you want shorter lease times, you'll have to hack the firmware or use an external DHCP server. I had to do that with busy system that was filling up the DHCP table far to rapidly, leaving no slots for additional clients. We were delivering routeable addresses (bad idea) so the available number of IP's was very limited.
I had a friend do some tweaking and set it up so that any DHCP renewal request always returns a negative acknowledgement at rebinding time. That would instantly expire the lease at the server at rebinding time and flush the table entry. No waiting for a timeout. The client would then search for a new DHCP server and get a new lease. That worked fairly well, but is rather nonstandard. It also had the side-effect of changing the IP address of all the users if all the leases were issued. Eventually, we gave up and just left it at 15 minute leases.
I haven't the slightest idea, especially since you didn't supply the make and model of the your router, your PDA, and any troubleshooting that you've done. However, I can speculate that if you turn off the PDA at night, and your router still has your PDA's MAC address in the DHCP table, it should reconnect exactly where it left off the night before. I do that on my own systems and find that I get the same IP address for days on end. Look at the IP status screen on the PDA and your unspecified routers log file page for any error messages.