[ih] The netmask

[John Day]

Yes, the network part was, in essence, a flat address space.  (Remember the Internet had already lost the Internet Layer.)

The blocks of IP addresses were handed out more or less in order regardless of who was requesting the block. Every block allocated required another entry in the router table. The network part did not exhibit any concept of ’nearness’ or locality. Until they went to assigning large blocks to Tier 1 providers and people had to get new blocks from their provider, the addresses did not exhibit locality and hence were not really addresses any more than MAC addresses were addresses. (Dalal in his paper on MAC addresses says that they knew the MAC address was really a device-id.)

And of course by this time, the “host” part wasn’t really just host addresses, i.e., enumerating the hosts, but if they were smart, it was the address space of the organization’s network that was assigned the block. And they assigned the addresses hierarchically to reflect nearness within their network to simplify routing.

In effect, the ‘host’ part was the network address and the ’network’ part was the internet address, instead they had have AS numbers for that.

Bottom line: Addresses belong to layers, not protocols. Protocols just carry addresses.

> On Jan 7, 2025, at 10:49, Craig Partridge <craig at tereschau.net> wrote:
> 
> 
> 
> On Tue, Jan 7, 2025 at 7:12 AM John Day via Internet-history <internet-history at elists.isoc.org <mailto:internet-history at elists.isoc.org>> wrote:
>> 
>> Prior to CIDR IP addresses were just flat identifiers.
>> 
> 
> We routed on the network part from the start.  And while officially the host part may have been flat, in practice it wasn't.  Everyone in network operations knew how to read net 10 addresses to figure out which IMP and port the host was on (and thus who to call if things went wrong).  As I recall, BBN's (and I think MITs and others) class B addresses used one byte of the host part for a subnet identifier (my first machine was on 128.89.1.XX -- which was a coax Ethernet hung off the first internal port of the BBN router in Building 6).
> 
> Craig
> 
> --
> *****
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