[mythtv-users] Static IP vs. DHCP

[Brian Wood]

Drew Tomlinson wrote:

> 
> To be pedantic,  DHCP and static (manual) IP configurations are like oil 
> and water.  They can not be mixed.  They can only exist side by side.  
> Thus, you can NOT use DHCP to configure a static IP address.  Static IP 
> addresses are assigned manually and configured on each client.  You CAN 
> use DHCP to dynamically assign and configure IP addresses on each 
> client.  And when you configure your pool of IP addresses from which a 
> DHCP server can assign, you can RESERVE specific addresses to be 
> assigned to specific clients when certain conditions are met such as MAC 
> address or host name.

True, to a point.

It depends on what you mean by a "static" or "dynamic" IP address, and
from whose point of view.

For example, my ISP provides me with "static" IPs (and charges me for
them) even though those addresses are assigned by the ISP's DHCP server.
I could set up the machines manually to use the addresses assigned by
the ISP, but in reality the "static" IPs are used by my routers, which
have DHCP servers that assign RFC 1918 addresses to my local machines.

"Static" and "Dynamic" from the point of view of the rest of the
internet are somewhat different from the same terms when used in the
context of my internal network.

In fact a lot of terms related to these matters have been abused. The
term "NAT" originally meant the dynamic assignment of "real"
(non-RFC1918) addresses, to conserve "real" addresses. The dynamic
assignment of RFC1918 addresses to local machines was originally termed
"IP Masquerading", but the term "NAT" is so commonly used now to refer
to the use of RFC1918 address that it is commonly found in router makers
specifications, even though the term is being incorrectly used.

A "static" address can change, and a "dynamically assigned" one can
remain static for years, the terms refer to how they were obtained, not
their longevity.

One might want to receive a "static" address from their ISP's DHCP
server so that any changes in the DNS servers will be picked up, though
it is possible to obtain that information without getting an actual
address, assuming a reasonable operating system (you couldn't easily do
that with a Windows box for example).

Things can get even more confused, I once had problems with router that
insisted on caching DNS calls, not a real problem except that the maker
didn't divulge that information in their docs.

IP addressing, and DNS are, or at least were at one time, so universally
mis-understood by PC users (most folks on this list know better) that
the ISP/router maker world tried hard to "unconfuse" their customers,
resulting in the end in even more confusion. How many "show you your IP
address" utilities simply give out the 192.168.x.x address assigned by
your router?

Just as hard drive makers finally figured out that if they print the
drive geometry on the device it will reduce phone calls, router makers
are finally starting to print the local default addresses on the boxes
or, in at least one case, making the router's internal DNS caching
respond to something like "http://router.net", a bad idea, at least if
you do not explain what you did.

The best bet is to make sure everyone understands TCP/IP addressing,
probably easy in the case of this list but impossible in the case of all
Windows users :-)

beww