Re: 127.x.x.x

I always understood this decision as representative of the shortsightedness that the original TCP/IP suite designers had about the need for IP addresses.

In all fairness to them, they had absolutely no concept of the IP applications that would emerge and the sheer explosion of consumed addresses that commerce (and porn!!!) would drive. Once they had arbitrarily (it would seem) selected a Class A IP address space for this function, they got stuck with that decision decade after decade.

I look forward to reading any more insight on the selection of the loopback address space.

Warmest Regards,

Anthony J. Sequeira, CCIE #15626
http://www.INE.com

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Q: Broadcasts are not used in IPv6. What is the primary replacement for this technology?
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On Apr 21, 2010, at 12:45 PM, Elias Chari wrote:

> It sounds like a huge waste of IPv4 addresses. I am puzzled as to why such
> RFCs made it to standards. Does anyone have a good explanation? Because I
> can't think of any
>
> Here is an extract from RFC 3330
>
> " 127.0.0.0/8 - This block is assigned for use as the Internet host loopback
> address. A datagram sent by a higher level protocol to an address anywhere
> within this block should loop back inside the host. This is ordinarily
> implemented using only 127.0.0.1/32 for loopback, but no addresses within
> this block should ever appear on any network anywhere
> [RFC1700<http://www.faqs.org/rfcs/rfc1700.html>,
> page 5]."
>
>
> --
> Regards,
> Elias
> CCIE#17354
>
>
> On 21 April 2010 13:38, Jack <ccie.unnumbered_at_gmail.com> wrote:
>
>> Thanks William.
>> As you mentioned, I am one of the old timers.
>> One decade ago, a CCIE showed me ALL IP addresses could be assigned to the
>> interfaces of the routers in his lab, including
>> 0.0.0.0/8 and 127.0.0.0/8. I regret that we lose the freedom.
>>
>> Also, thank you for the tip on linux box
>>
>> Jack
>>
>>
>> William McCall wrote:
>>
>>> No.
>>>
>>> For at least 2 reasons:
>>>
>>> 1) RFC 1700 [1] and RFC 3330 [2] both specify that the 127.0.0.0/8
>>> should never appear on any network anywhere. Cisco complies with this
>>> directive [3] in 12.4T (and, I'm willing to bet, most any other
>>> version of IOS but the old timers can tell me about how 11.0 allowed
>>> this)
>>>
>>> 2) These loopback addresses are used internally for, primarily,
>>> service modules and linecards (anyone, is there any other place this
>>> is used?) and would most likely break stuff. For example, attaching to
>>> a line card on the 12K GSR (IOS, not sure about XR) results in a funky
>>> telnet connection to an address like 127.0.0.17.
>>>
>>> For the scenario you proposed on your Linux box before, you can create
>>> a sub interface on the loopback interface. Example:
>>>
>>> ifconfig lo:0 192.168.12.1 netmask 255.255.255.0
>>>
>>> And now you have a new network for handling your terminal server.
>>>
>>> HTH
>>>
>>
>>
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Received on Wed Apr 21 2010 - 14:01:15 ART