mogul@DECWRL.DEC.COM (Jeffrey Mogul) (01/26/89)
From: mcneill@eplrx7.UUCP (mcneill)
One machine on our LAN caused a lot of havoc. It was mistakenly placed on
the network before it's networks file had been configured correctly. It
thought that it's network address was 192.9.200.0. I seem to remember
seeing somewhere "never use x.x.x.0 address" (where x ranges from 0 to
255). Is my memory correct? If that is an untouchable address why is it?
I thought we had put this prohibition into RFC950, but on a quick read
I couldn't find it (we did prohibit subnet number 0).
Anyway, I can tell you why you shouldn't do it: because in spite
of the standard for broadcasting (RFC919) which specifies the
use of an ``all-ones'' broadcast address, many hosts (derived
at some point from 4.2BSD) still use the x.x.x.0 address for
broadcasting (if they also understand subnets, that is).
So, using x.x.x.0 or x.x.x.255 is likely to confuse some hosts
and perhaps lead to broadcast storms ... which you don't want.
-Jeffnarten@PURDUE.EDU (Thomas Narten) (01/26/89)
> One machine on our LAN caused a lot of havoc. It was mistakenly placed on > the network before it's networks file had been configured correctly. It > thought that it's network address was 192.9.200.0. I seem to remember > seeing somewhere "never use x.x.x.0 address" (where x ranges from 0 to > 255). Is my memory correct? If that is an untouchable address why is it? >I thought we had put this prohibition into RFC950, but on a quick read >I couldn't find it (we did prohibit subnet number 0). It may not have made it into the Subnet spec, but gateway requirements RFC-1009 says: (section 2.1): ... There are certain special cases for IP addresses, defined in the latest Assigned Numbers document [23]. These special cases can be concisely summarized using the earlier notation for an IP address: ... The following two are conventional notation for network numbers, and do not really represent IP addresses. They can never be used in an IP datagram header as an IP source or destination address. (h) {<Network-number>, 0} Specified network (no host). (i) {<Network-number>, <Subnet-number>, 0} Specified subnet (no host). Note also that the IP broadcast address, which has primary application to Ethernets and similar technologies that support an inherent broadcast function, has an all-ones value in the host field of the IP address. Some early implementations chose the all-zeros value for this purpose, which is not in conformance with the specification [23, 49, 50].