determining if host has a dynamic or static ip address

Polytropon freebsd at
Tue Jun 9 01:21:36 UTC 2020

On Mon, 08 Jun 2020 19:34:17 -0400, Ernie Luzar wrote:
> I am asking if anyone knows of a way to determine what type of public ip 
> address the host has been ISP assigned [...]

That's not exactly easy to tell. You can examine the hostname
associated to the IP, and maybe it contains something like "pool"
or "dynamic" - in that case, it's usually a dynamic IP from a
specific range.

There are ranges allocated by the ISPs that they use as a pool
for customers' addresses assigned via DHCP (or a different means),
for example. You can check if the IP is in such a range. Again,
it's up to the ISP how they use such a range, as they could use
a subset for addresses that they actually use as static IPs.

The "rinse & repeat" method is also not reliable: You could
disconnect and reconnect to your ISP, and if you get a different
IP each time, it's probably dynamic. If not, it can still be
assigned dynamically, so no way to be sure. Some ISPs sometimes
"bind" the dynamic IP to the MAC address of the endpoint (and
some even use the MAC address as the authentication factor for
the customer).

More information here:

> [...] by coding a csh script?

Why should anyone do this in _C_ shell?!

Tom Christiansen: "sh Programming Considered Harmful", 1996

I know what I'm talking about, I exactly wrote (and still use)
one, in numbers: 1, C shell script. ;-)

> Is it even possible?

Depends. :-)

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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