On 25/05/10 08:47 AM, James Carlson wrote:
Garrett D'Amore wrote:
On 5/25/2010 6:56 AM, PRDEEP KUMAR wrote:
Hi Experts,
Am new to the networking.Is there any specific reason why
only 127.0.0.1 is used as a loop back address,why not other addresses.
Historical convention? The standards say that 127/24 is reserved for
loopback addresses.
It's actually /8. See RFC 1122 section 3.2.1.3(g), which describes an
entire Class A for loopback.
You could use any other 127 address, I suppose (and
I've done so), but I suspect 127.0.0.1 is so firmly entrenched in the
minds of admins and developers that you'd probably find things that
break if you tried a different address.
Long ago, at a company far away, we were able to use 127.x.x.x for
private communication among a collection of interconnected machines by
configuring Ethernet interfaces with addresses like 127.1.0.1/24 and by
reconfiguring lo0, which normally is configured as 127.0.0.1/8, with
127.0.0.1/24 instead. It actually worked, and allowed customers to use
the rest of the interfaces for any legal IP address, though it wasn't
what you might call "standards conformant."
I don't know of anyone who has changed lo0's address away from 127.0.0.1
... nor any reason to do so. I suspect that wasn't the original
poster's intent, though.
I tried that... about 6 years ago with BSD but it took a few
changes to disable various assumptions about where a packet
with a 127/8 address could come from. I think the most annoying
one was that code threw away LOOPBACK_NET packets if the
interface used was not also marked with the IFF_LOOPBACK flag.
It's the type of thing that you could easily imagine as being
possible with the etherstub device and vnic's attached to
it and supporting various zones with opensolaris. I suspect,
however, that it wouldn't be quite that easy...
Darren
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