[unisog] Public or Private IP addresses?

John Kristoff jtk at northwestern.edu
Fri Oct 14 00:20:51 GMT 2005

On Thu, 13 Oct 2005 17:43:51 -0500
"Stejerean, Cosmin" <cosmin at cti.depaul.edu> wrote:

> DePaul University uses public IP addresses for all of the computers on
> campus. I have heard from people at other universities that they use
> private IP address ranges internally and then map private to public IP
> ranges.

Oh no... *a DePaul ghost cringes*

> I am wondering how the network is setup at other universities and what
> people on the list think about advantages and disadvantages of picking
> one over the other.

There have been a bazillion public versus private address discussions
on numerous lists I'm sure you can find all the talking points
eventually without too much trouble.

Most tier-3 schools (whatever that means) and larger tend to have had
public space from a legacy allocation (before the whole RIR structure
was put in place).  These netblocks were class-based a and usually a
school got at least one class B (/16).  Some have more than one (such
as northwestern.edu) and a few of the very early ones even got a /8
like mit.edu).  It is probably a safe bet that by and large these
fortunate universities still use their public addresses for most
applications and many still use those addresses exclusively.  Some
organizations have opted to deploy private addresses for select causes
such as facility operations type devices (e.g. physical access controls,
environmental systems, and surveillance).  Usually this is done to
add in an inherent stumbling block in accessing these systems directly
from outside the organization.

Personally I think private addresses should generally be avoided.
I think this is especially true if you have a large pool of public
addresses like many educational institutions do, but not everyone
feels this way.

There are numerous advantages and disadvantages to each scheme and
I'll let others enumerate those points if they want to, but I'm going
to avoid going down that rat hole on the list.


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