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why loopback testing having so long range

Posted on 2003-12-02
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Last Modified: 2012-05-04
hi guys!
 i have a question in mind hope anybody will answer.
question is why Loopback testing is being assigned a big range of ip addresses 127.x.y.z ???
as we can do this testing with the single ip address then what could be the reason to assign this big range.
i'll appreciate comments with some reference to study about.
thanking you in anticipation.
bye.
Faysal.
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Question by:xqzme_plz
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by:Bing CISM / CISSP
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good question. quoted from RFC 1166:

The class A network number 127 is assigned the "loopback" function, that is, a datagram sent by a higher level protocol to a network 127 address should loop back inside the host. No datagram "sent" to a network 127 address should ever appear on any network anywhere.

as for the reasons of why use a class A network number, IMO, 3 reasons:

1. historical limitation
2. easy implementation
3. reserved for future use

hope it helps,
bbao
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by:xqzme_plz
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i couldn't understand the following in ur comments

IMO
and could u plz give me the links where i can find some details about the reasons like historical limitatation as its not clear yet what are those historical limitations
and it would be more easier if a single ip address will be there for loopback testing rather than a big range of ips
and what type of future use ? cuz there are millions of ip addresses and now we are adopting ipv6 so again its quite confusing

i searched out the Experts-Exchange database and i found a question same like i quoted but i couldn't open that page as im not a premium member ...it means it already been accepted by somebody so i'll appreciate if sumbody will give me that accepted answer or give me some links which containing more details about this issue.
thanks
Faysal
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by:Bing CISM / CISSP
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IMO = In My Opinion. Could you please give me the key words of your search? I can find the KB for your.
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by:chicagoan
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The IPv4 address space was originally carved up into
Class A addresses begin with 0xxx, or 1 to 126 decimal.
Class B addresses begin with 10xx, or 128 to 191 decimal.
Class C addresses begin with 110x, or 192 to 223 decimal.
Class D addresses begin with 1110, or 224 to 239 decimal.
Class E addresses begin with 1111, or 240 to 254 decimal.
Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine.
While 127.0.0.1 is commonly used, it's not sacred - any address beginning with 127 is reserved, it's a waste but the designers thought this would be an inexhaustable pool, they didn't envision the growth of the personal computer.


KEN OLSON
Founder and president of Digital Equipment Corporation    
"There is no reason anyone would want a computer in their home."

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by:xqzme_plz
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bbao the keyword was "loopback" and i selected networking section+all the sub sections or u can select the all topics
and it will be on the top of search.
and chicagoan could u plz find me out some valid refences where officals or internet authorities has written some comments over this stack 127
thanks.
Faysal
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by:Bing CISM / CISSP
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you mean this one?

why do we always have 127.0.0.1 as destination address for loopback interface?
http://www.experts-exchange.com/Networking/Q_20460140.html
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by:InteraX
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Another thing to note, was that when this was designed, subnetting was not necessarily possible. As the 127.x.x.x network is a standard class A address range, it would have recieved a default subnet mask of 255.0.0.0. This would mean that they had to assign the whole 127.0.0.0-127.255.255.255 address range to the loopback system. Early implementations of IP did not have the subnet mask and only relied on the ip address to creat broadcast domains etc.

Sorry, not necessarily the clearest of exp[lanations, but should cover the historical side.
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by:chicagoan
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by:xqzme_plz
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hmmm ok so many things are clear now .. some of with the reference of bbao
and others with chicagoan.
but still in the RFC's too they didn't clear about the rest of the bulk of ips.. they said usually 127.0.0.1/32 is used but any traffic directed to that network will be considered for the loopback purpose and can't be appear on the network. if they can't appear on the network then whole of this range is wasted for no reason. in fact the base of my question was to find out the reason behind this wastage of a big pool .. it can be from the Class C so that less ips would be wasted so they are not mad to destroy a biggy pool the question is there must be something behind the scence and what is dat smthing we'll have to discover it.
i'll read-out more about it and if u guys found some more links please send and then i'll close this question .
thanks
Faysal.
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Bing CISM / CISSP earned 180 total points
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hi, let me try explan more for my first post, again, as i said it is IMO, which means it is my personal viewpoint:

1. historical limitation: there is no MASK in the first implementation of tcpip, that means network nodes use the first number to distinguish network size and host ID. moreover, since class A is determined by its first octet, the higher-order bit is 0, so 127.x.x.x (01111111.x.x.x) is the latest segement of class A addresses. people often use all zero or all one numbers for special usages, reserving a class A segment is for maximum flexibility. hmm, so we can not see a class B loopback segment nowadays, hehe. ;-)

2. easy implementation: as what i say above, there was no MASK concept in early days, segment addess 01111111.00000000.00000000.00000000 is easy to be determined by AND/XOR operations quickly and easily. even nowadays, such pattern is still easy for matching subnets by applying XOR operation.

3. reserved for future use: class A has 1,677,216 hosts, so it allows people have more space to divide it into a lot of reasonable zones for specific usages, different devices, systems and applications.

4. another reason, maybe those people used tcpip early never thought tcpip based network could span all over the world, and the addressing space is so limited for today's applications. hmm, it sounds this point should be one of historical limitations too. :)

hope it helps,
bbao
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by:xqzme_plz
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thx bbao now this time its quite a satisfactory reply as you explained what you told me in ur 1st comments.
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by:chicagoan
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"B" !
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by:Bing CISM / CISSP
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grade b for "quite a satisfactory reply"? :o) if the my posts are not correct enough, any comments are welcome.
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by:chicagoan
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I loved your posts!

robbed I say!
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by:xqzme_plz
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im really sorry i dont know about the grading tech i should have read about it.
tell how may i increast it ?
and i m also willing to give some extra points for my negligence
im sorry again.
Faysal.
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