Yesterday, one of our architects popped into my office and we had a brief discussion about blocklists. The topic shifted to how many IPs we have banned over the years.
The total number of available IPv4 IP addresses is 232, or 4,294,967,296 different ones (4.3 billion). He then said that the actual number is less than that since there are non-routable IP addresses. I don't know the exact details, but that actually drops the number of IP addresses in half to 2.1 billion. If anyone knows anything more about that, please let me know because I'm drawing a blank at the moment.
Since October 2006, we have a list of IP addresses that we have banned from our network at one time or another. We're only Exchange Hosted Services, we're not one of the big mail providers like Hotmail, Yahoo, or AOL. Simply going by our own list of IPs from our own private list (ie, not a 3rd party list like Spamhaus), we have blocked 1.5% of the total available IP addresses, or 3% of the IP addresses if you use the scaled down figure.
That's a heck of a lot of IPs to ban in a relatively short period of time.
PingBack from http://geeklectures.info/2008/01/09/just-how-many-ips-are-spamming-anyhow/
Spammers love to hack a router in Asia (where it's easy to do it), route a non-routed Class-C there, they use every available IPs on it before dropping the route.
They also love to use botnet who consists in spywares installed on a lot of home/offices computers to send spam directly from them.
But with tools like SPF, DNSBL, MX verification & reverse DNS look-up, you can avoid most of this type of spam easily, since most of the allocated IP a on dynamic black-list and non-routed Class-C does'nt usually have any reverse look-up zone...
This is a follow up to my previous post .  I recently looked up an old version of the PBL and decided
"He then said that the actual number is less than that since there are non-routable IP addresses. I don't know the exact details, but that actually drops the number of IP addresses in half to 2.1 billion. If anyone knows anything more about that, please let me know because I'm drawing a blank at the moment."
Are you still wondering about this? The routable addresses are slightly more than half. Parts of IP space are reserved for various purposes, and so are not routable. Look up "broadcast" and "IANA reserved" or "private network"; a basic book on TCP/IP should cover these topics.
Hope this helps,
Ah, yes, thanks era. I couldn't remember the details of non-routable addresses. I'll take a look.