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after "ipconfig /release" I myself am unable to initiate connection to a remote ip, such as using the browser. But can an attacker across the network initiate connection to my ip?

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up vote 1 down vote accepted

If you do an ipconfig /release and your IP is removed, then your system's TCP/IP stack is not going to pass through any traffic to applications using TCP/IP from any interfaces without IP addresses. Note that ipconfig /release doesn't affect interfaces that have a static IP set, so those interfaces would still have a manually set IP./

If an attacker continues to send traffic to that IP, your network card does receive it, but your system's TCP/IP stack (and your network card) won't consider it as destined for that system, and therefore won't grab it - the traffic will never make its way up to the application listening on specific TCP or UDP ports.

But, if the NIC is put into promiscuous mode I believe it is possible to continue to pull raw Ethernet frames or IP packets off the card - WinPCap does something like this - but this is really in a sense bypassing the TCP/IP stack. But you need very specific software doing this type of thing. Standard network applications that just listen on specific TCP or UDP ports can't receive any traffic in this situation.

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this makes good sense, thanks – EndangeringSpecies Mar 6 '12 at 6:26

If your computer does not have an IP address it cannot be reached using TCP/IP. However, you may have other protocols running. IPX perhaps? A reboot would likley allow the system to obtain an IP again.

Then the network srup will also have an impact. If you are behind a firewall, that has an impact.

More info on your concern would assist.

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does my computer really have no ip address after this, as seen from outside? FWIW I am located behind my own wifi router, and I notice that /release executes very fast (/renew takes longer). What would happen if attacker sends me a message to ip address observed from before /release? – EndangeringSpecies Mar 5 '12 at 16:10
If you release all of your adapter then you won't have an ip address. – Ramhound Mar 5 '12 at 17:42

When you run ipconfig /release your local address (assuming that you are connecting over a router) will be released. It means your computer will not have a valid IP address to send or receive packets from/to your router. It would "isolate" you against an attack, however you must know that IP address belongs to the 3th layer of the OSI model, and you still have a valid MAC adress available on your interface and you computer will keep receiving ethernet frames from your local network(assuming that you have a switch) and another computer from your local network can be a "gateway" to an attacker.

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