Re: Why can't I sendto() to 127.255.255.255

Abraham K. Mathen wrote:
NOTE : A copy of this message was sent to freebsd-hackers also.
Apologies for the separate mails.

Hello freebsd-net,
I wrote a short program (on FreeBSD 6.0), that attempts
to call sendto() on a UDP socket, with 127.255.255.255 as
the destination address. It failed - with errno 49 (EADDRNOTAVAIL).
Setting SO_BROADCAST and IP_ONESBCAST did not help.

After examining
- various RFC's,
- source code under /usr/src/sys/netinet/ and
- archives of freebsd-hackers & freebsd-net,
I have not been able to determine the reason.

Is it possible to successfully sendto() on a UDP socket
with 127.255.255.255 as the destination address? If yes,
how can that be done.

Specific questions :
----------------------------------------------------------
- Is it correct to understand that 127.255.255.255 is the
directed network broadcast address for net 127? If yes,
which RFC specifies that?

- If not, is 127.255.255.255 considered to be a host
address? If yes, which RFC specifies that?
----------------------------------------------------------

As far as I am aware the only RFC's that define the 127.0.0.0/8 block
are rfc3330 which states,

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

and rfc1122 which says:
{ 127, <any> }

Internal host loopback address. Addresses of this form
MUST NOT appear outside a host.

I would interpret this as 127.0.0.0/8 are all loopback host addresses,
but I'd be happy to be corrected.


Vince

Could you please help me understand this?


sincerely

Mathen
(Abraham K. Mathen)

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