Re: 127.x.x.x

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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