Just how static is that IP address?

Steven W. Orr steveo at syslang.net
Mon Jul 3 22:12:00 EDT 2006


On Monday, Jul 3rd 2006 at 16:34 -0400, quoth Ted Roche:

=>TDS is offering their business customers (well, at least this one) a static IP
=>address at what appears to be a fair price. I know that a static IP is set in
=>the network stack, and there's no need to run a DHCP client, since the IP
=>address isn't going to change. This opens up some opportunities that we more
=>challenging with dynamic IP addresses.
=>
=>I understand some mail services reject email that claims to come from an email
=>server on a dynamic IP address on the theory that most of these dynamic
=>addresses are used by considers without the license from the ISP to run said
=>server on their machines; 99% are likely Windows machines taken over by
=>malware sending spam, while 1% are home based businesses and hobbiests who
=>haven't figured out how to relay through their ISPs.
=>
=>Here are my questions: how do the big email services distinguish dynamic from
=>static IPs? Is there a great big list somewhere listing the 256^4-2 addresses?
=>Is there a way I can determine if the address I get is "really" static (if
=>there is such a thing) or should I just try to set up a email server and see
=>if I can get through to dad at aol.com?

1. A so-called static address may be allocated from a dynamic pool. That 
means that people who use RBLs to distinguish you from the real static ips 
may reject your mail. In sendmail that's why they have the mailertable.

2. You will still need to use a DHCP client. Just because they promise not 
to change your address doesn't mean the address you have doesn't need to 
be renewed every 8 minutes.

3. Reverse DNS. I got it but only by luck. Don't tell anyone.



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