Are you talking about dynamic local IP address or dynamic external IP address?
If you are talking about an address like 192.168.1.3 address (local address) the commands you mentioned should work. If you don't get a different one is because the router assigns addresses in ascending order, and if you release the address, if the router doesn't have any lower IP addresses, it will assign the same address. The router will delete the lease as the PC tells the router to release that IP address and basically it tells the router "I'm done with this IP, you can have it back".
If you are talking about an address like 69.14.66.10 (public) you must either reboot the router, or re-start its interface (if its a router like a cisco router that you can go into its interface and do -shutdown- and then -no shutdown-. For this though, nothing you can do from Windows.
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by: ecsrdPosted on 2009-08-20 at 20:34:47ID: 25148958
You won't be assigned a new IP since the router already associates your MAC address to one that was already in its database recently (before the timeout). As long as the address cache is not flushed on the router you'll get the same address back. HOWEVER, what you CAN do to force a different IP is to change your IP to a static address and then back to DHCP - what this will do (if the DHCP address is not in use and is part of the scope your router assigns) is cause the router to issue you the IP that you had assigned statically via DHCP.
The way DHCP servers work for handing out IPs is like this:
Normal operation:
New client requests an IP
Lowest available IP in the scope is assigned to the client
Client lease expires
client requests a new lease
same previously leased address is reassigned
Contention Mitigation - new IP lease:
Client leases an IP after being previously assigned a static IP in the same range as the DHCP scope
DHCP issues the same IP if already not in use
Contention Mitigation - early lease renewal:
Client releases its existing IP address and requests a new address
DHCP issues the same address if available that the client previously retained to prevent the DHCP scope from issuing all available IPs to one client.
I hope this helps.