tcp-ip@ucbvax.ARPA (07/28/85)
From: Charles Hedrick <HEDRICK@RUTGERS.ARPA> We have heard a rumor that some people consider subnet zero to be illegal. Since our current hosts are 128.6.0.x, and we are about to need to move to subnetting, this is an obvious concern to us. We haven't seen this in the proposed subnet RFC, but it has shown up in one piece of code that claimed to implement subnetting. As I read it, there is special meaning attached to 0.0.0.0 - I don't know who I am 0.0.0.x - i.e. all bits under the subnet mask (network number plus subnet number) are zero - I don't know what net I am on x.y.z.0 - I know what net I'm on, but not who I am But I do not see any constraints on the subnet number itself. Am I missing something? -------
tcp-ip@ucbvax.ARPA (07/29/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> This is being discussed by the group that did the subnet change to the IP architecture. The general feeling in that group is that subnet '0' should be non-legal (i.e. reserved for future use). This follows the precedent in the IP architecture where all 1's and all 0's either have special meaning or are preserved. This restriction will probably be in the extended subnet specification document (to appear soon). Noel -------
tcp-ip@ucbvax.ARPA (07/29/85)
From: Mark Crispin <MRC@SIMTEL20.ARPA> Duh, what does this mean for class B 1822 networks? The byte that is normally used for a subnet is the host number on the IMP, e.g. 128.43.0.2 is DREA-XX, host 0 on IMP 2 of DRENET. We could perhaps change the addressing of DRENET to swap those bytes, so that DREA-XX would become 128.43.2.0. It would be more logical that way. On the other hand, that sort of thinking would argue that ARPANET and Milnet should also have a flag day and migrate from the current net.host.local_port.IMP to net.IMP.host.local_port. Basically, what I am saying is that I expect that no ban be placed on class B addresses with 0 in the third octet. What is done in the subnet system is one thing, but it must NOT be made a rule outside of it. -------
tcp-ip@ucbvax.ARPA (07/30/85)
From: Jeff Mogul <mogul@Navajo> My gut feeling is to side with Noel (zero subnet numbers are illegal), but on reflection I am compelled to agree with Jon (zero subnet numbers must be supported to preserve compatibility.) However, I suggest that we "strongly recommend" against assigning new zero-numbered subnets. I say this uneasily, because I can think of all sorts of minor reasons why reserving zero is a good idea. Note that on the issue of all-ones subnets (all bits in the subnet field set), I think the need for broadcasting support (whether or not all organizations intend to use it) outweighs any compatibility argument -- especially as there currently seem to be few hosts that would fall afoul of a prohibition against all-ones subnet numbers. -Jeff
tcp-ip@ucbvax.ARPA (07/30/85)
From: CERF@USC-ISI.ARPA Mark, I'm with you on that point - to the extent that some of the address formats encapsulate what turn out to be physical addresses, we certainly cannot arbitrarily rule out the value 0 when it is a component of a valid embedded physical address. Of course, had all the IP addresses been "logical" and mapped in some fashion (who on earth would maintain the table???) then this might be less a problem. Vint
tcp-ip@ucbvax.ARPA (07/30/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> I don't see how this conflicts with what I said: there is some possibility that the use of *subnet* 0 will be disallowed. -------
tcp-ip@ucbvax.ARPA (07/30/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> I think there are as many sites with subnet FF in use as there are with 0. I don't see that migrating hosts out of the potential subnet 0 before turning subnetting on is a big deal. -------
tcp-ip@ucbvax.ARPA (07/30/85)
From: Jeff Mogul <mogul@Navajo>
I think there are as many sites with subnet FF in use as there
are with 0. I don't see that migrating hosts out of the potential subnet
0 before turning subnetting on is a big deal.
I count 6 hosts in the NIC host table with (for address A.B.C.D) any
of A, B, C, or D = 255. One is MITRE, the other 5 are all at LBL.
Of course, there may be hosts not listed with the NIC, and there
may be collisions on other addresses if somebody uses subnet
fields which are not 8 bits wide, but there are clearly far more
hosts with all 0s than all 1s where subnet fields might go.
I'd vote with you for changing the host addresses (it isn't THAT
big a deal) to allow banning of all 0s subnet numbers, but I suspect
we'd lose the vote.
-Jefftcp-ip@ucbvax.ARPA (07/30/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> Mark, I don't understand what you think you are disputing. It is perfectly legal for any network *without subnets* to have 0's in any part of the 'rest' field. Nobody ever said otherwise. I was only discussing the case where subnets *were* in use. Noel -------
tcp-ip@ucbvax.ARPA (07/31/85)
From: Mark Crispin <MRC@SIMTEL20.ARPA> Damn it, if the network doesn't have subnets it should have whatever it damned well wants to in its octets!!! I would like to see you have ARPANET and MILNET have a flag day...after all, they can have 0 in the second and third octets. Or are they exempt? I know that a number of sites are host 0 on an IMP deliberately just so the users can say @O <n> without dots, colons, slashes, whathaveyou. -------