Using the Loopback Interface to simulate a DMZ

Posted on 2003-03-12
Medium Priority
Last Modified: 2013-12-15

I need a detailed explanation of what the loopback interface is and how it works. If my IP address is and the loopback interface is how to they relate to each other? I know that both will allow me to view web pages on my machine with web services running but I dont know how they differ or how they compare or how they really work.

I also need to simulate a DMZ/lan environment and setup a simple firewall with the loopback interface as part of the DMZ and the assigned IP as part of the protected lan environment. Can you explain this concept to me? It is worth alot of points if you can.

Question by:webnso
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Accepted Solution

naccad earned 300 total points
ID: 8122810
loopback or is a special case, actually the whole
subnet ( is a special case.

its there to point to "myself", if you ever did C++, it
resembles the "this->" pointer.

127.0 is not accessible from anywhere except "this" machine

an external IP like is just that, external,
the outside world can see it, can access it,...etc.

you cannot use loopback as part of a DMZ or of anything
loopback should be totally open to loopback, i.e.

localhost <-> localhost allow any any

or else a LOT of things will stop working.


Assisted Solution

majorwoo earned 300 total points
ID: 8146355
to slightly complicate things       to     to    to    to

those ranges of addresses are reseerved for "internal" use, not valid for the internet itself, but usefor for private LAN's.  So we end up with 3 sorts here, the loopback which is correct, is used only for "this" computer. The "private" addresses above used only for talking to machines on your LAN and not out onto the internet. And all other addresses, "external" that are considered good or routable by the internet.

Ok, that's my .02 ;-)

Expert Comment

ID: 9076639
This old question needs to be finalized -- accept an answer, split points, or get a refund.  For information on your options, please click here-> http:/help/closing.jsp#1 
Post your closing recommendations!  No comment means you don't care.
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Author Comment

ID: 9080599
Delete this question and refund points, no acceptable answer was received.

Expert Comment

ID: 9080634
you have a pretty good explanation of IP address schemes here...

Author Comment

ID: 9262384
Please refund points for this question, the topic is way over my head and no one can explain it to me in a manner that I can comprehend. I gave up a long time ago and have moved on to other things. I appreciate people trying to help, but there is too much I dont understand .... and probably never will.....


Expert Comment

ID: 9266999
I don't agree.  The explanation of IP's provided is about as low level as you can get for a somewhat complex topic.  Webnso never returned to ask for clarification which either naccad or myself would have provided.


Author Comment

ID: 9267786
The purpose of this question was to determine what and how the loopback interface worked. I am telling you that this topic was over my head and that none of the answers made sense to me.

When did you become me??

You are the expert, so of course it makes sense to you.......

I dropped that class and havnt looked back, that is why I am not interested in discussing it further.

Author Comment

ID: 9267855
I have NO desire to bicker about another question so please make this GO AWAY any way you see fit!!!!!!!!!
I will send any more replies i get to Trash.


Expert Comment

ID: 9268054
I'm not interested in a flame war, and I was not intending to insult you.

I simply said the explanation is correct, and if you wanted more clarification you could have asked.

Expert Comment

ID: 9291400
webnso and majorwoo answered the question correctly.  Asker did not provide feedback. Split points between webno and majorwoo.

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