On Wed, Jun 26, 2019 at 1:20 PM David Miller <da...@davemloft.net> wrote: > > From: Dave Taht <dave.t...@gmail.com> > Date: Sat, 22 Jun 2019 10:07:34 -0700 > > > The longstanding prohibition against using 0.0.0.0/8 dates back > > to two issues with the early internet. > > > > There was an interoperability problem with BSD 4.2 in 1984, fixed in > > BSD 4.3 in 1986. BSD 4.2 has long since been retired. > > > > Secondly, addresses of the form 0.x.y.z were initially defined only as > > a source address in an ICMP datagram, indicating "node number x.y.z on > > this IPv4 network", by nodes that know their address on their local > > network, but do not yet know their network prefix, in RFC0792 (page > > 19). This usage of 0.x.y.z was later repealed in RFC1122 (section > > 3.2.2.7), because the original ICMP-based mechanism for learning the > > network prefix was unworkable on many networks such as Ethernet (which > > have longer addresses that would not fit into the 24 "node number" > > bits). Modern networks use reverse ARP (RFC0903) or BOOTP (RFC0951) > > or DHCP (RFC2131) to find their full 32-bit address and CIDR netmask > > (and other parameters such as default gateways). 0.x.y.z has had > > 16,777,215 addresses in 0.0.0.0/8 space left unused and reserved for > > future use, since 1989. > > > > This patch allows for these 16m new IPv4 addresses to appear within > > a box or on the wire. Layer 2 switches don't care. > > > > 0.0.0.0/32 is still prohibited, of course. > > > > Signed-off-by: Dave Taht <dave.t...@gmail.com> > > Signed-off-by: John Gilmore <g...@toad.com> > > Acked-by: Toke Høiland-Jørgensen <t...@redhat.com> > > Applied, thanks for following up on this.
This breaks an undocumented feature of Linux: $ telnet 0.0.0.1 22 Trying 0.0.0.1... telnet: Unable to connect to remote host: Invalid argument It's sometimes useful to put 0.x.x.x in command-line flags, /etc/hosts, or other config files, because it forces connect() to fail immediately, instead of sending packets and waiting for a timeout. Given that this has been user-visible for decades, is it a good idea to pull out the rug?
