From owner-freebsd-hackers Fri Mar 31 9: 8:46 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from ludwig.troikanetworks.com (host03.troikanetworks.com [12.31.172.3]) by hub.freebsd.org (Postfix) with ESMTP id 1F0B237BFC8; Fri, 31 Mar 2000 09:08:41 -0800 (PST) (envelope-from ericp@troikanetworks.com) Received: by host03.troikanetworks.com with Internet Mail Service (5.5.2650.21) id ; Fri, 31 Mar 2000 09:08:47 -0800 Message-ID: From: Eric Peterson To: 'Tony Finch' , nik@freebsd.org Cc: hackers@freebsd.org Subject: RE: No route for 127/8 to lo0 (?) - another use for loopback subn et? Date: Fri, 31 Mar 2000 09:08:39 -0800 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset="iso-8859-1" Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Tony Finch [mailto:dot@dotat.at] wrote: > Nik Clayton wrote: >> >> I thought that 127/8 was the "local net", and that >> packets sent to any of those addresses would go via >> the loopback interface. That seems to be how Linux >> and Windows 98 do things (the only systems I can >> check this on at the moment). Assuming that's the >> case, why does FreeBSD only add a a host route to >> 127.0.0.1, and not a network route for 127/8? > > I did some further investigation to see how old this > oddity is and it seems to be the way BSD has always > handled the loopback interface. There's an explicit > exclusion in the interface initialization code in in.c > that gives loopback interfaces a host route instead of > the network route that a normal interface gets and it's > been that way for 15 years. I always thought it was a great waste of network address space to devote an entire class A network to a single loopback address. An idea I got from a co-worker a while ago was to allow the 127.* (or some smaller subnet of 127) to be devoted to "intra-box addresses", for example: 1. A cluster of devices/slots within a chassis 2. A parallel processing machine 3. A multi-processor computer/device All of the above may have inter-processor communications that do not need to leave the chassis. Analogous to how the 192.168.* (RFC1918) addresses are used for intranets, these addresses wouldn't be allowed to be seen by the outside world (i.e. outside the "chassis"), but would permit internal IP communication without having to waste (and configure) a "real" IP net number. If these devices needed to get to the outside world, they could use NAT (again, analogously to the RFC1918 case). Regards, Eric -- Eric Peterson ericp@troikanetworks.com (805) 370-3046 PGP: http://pgp5.ai.mit.edu:11371/pks/lookup?op=get&search=0x4DA8EEF1 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message