question posée sur  Moorcock's miscellany à  un informaticien administrateur :

[quote:zpegdzhy]David : in fact i would ask you a question :

On a forum, if you banish a full IP adress, you banish only the owner of the adress, not all IP sharing the same suffix or prefix ? 

for instance if i banish : 00.200.100.60 ( a false IP adress used as exemple ) 

i don' t banish every ip with 00 as prefix or 60 as suffix ?[/quote:zpegdzhy] 

réponse : 

[quote:zpegdzhy]MK, normally you banish the IP address as stated. Let me see if I can explain...

Network computers (that's the only one that can get an IP address - i.e. if it's not on a network/Internet it doesn't need an IP address) usually get IP addresses from DHCP servers. So, a PC comes online and fires off a request to the DHCP server for an IP address. The server has a range of addresses that it can dispense, let's say, 100.200.100.001 - 100.200.100.255, and issues out 100.200.100.010 to the requesting PC.

If you ban 100.200.100.010 that won't affect 100.200.100.001-009, or .111-255, but if you ban 100.200.100.x then that will affect all PCs with addresses in that range. Likewise, banning 100.200.x.x will affect an even larger number of IP addresses.

The thing to bear in mind is that DHCP stands for Dynamic Host Configuration Protocol. 'Dynamic' means that the IP address isn't 'static' and that it can (and probably will) change.

So, going back to our PC that requested an IP address and got 100.200.100.010... IP addresses are usually issued on a leased basis, say, 3 days, after which they expire. When they expire, the PC requests a new IP address from the DHCP server. Now, often - unless you get a burst of addresses expiring at the same time - the server may just re-issue the IP address the PC just had, but that's not a guarantee. So there's a good chance that eventually the PC will get a different IP address than the one you banned. That's why you may want to ban an range of addresses rather than just one.

Hope that helps somewhat.[/quote:zpegdzhy]

donc banir une adresse complète fait courir un risque très limité,surtout si le serveur est  à  l' étranger !