IP address classes vs CIDR (was Re: Reviving ARPAnet)

Eric Smith spacewar at gmail.com
Thu Jan 18 13:53:00 CST 2018

On Thu, Jan 18, 2018 at 11:35 AM, Grant Taylor via cctalk <
cctalk at classiccmp.org> wrote:

> On 01/18/2018 11:00 AM, Eric Smith wrote:
>> Years ago I added a configurable "bozo-arp" feature to the Telebit
>> NetBlazer router, which would respond to ARP requests for non-local
>> addresses and reply with the router's MAC address (on that interface),
>> specifically in order to make classful-only hosts work on a CIDR network.
> That functionality sounds exactly like my understanding of what Proxy ARP
> is supposed to do.

Proxy ARP is (or was, at the time) something that had to be configured for
individual IP addresses or ranges. What I did was have it reply to an ARP
for _any_ IP address outside the subnet(s) configured on that interface.

Since you stated that anyipd "…would respond to ARP requests for non-local
> addresses…" I"m assuming that you are talking IP and not another protocol.

Yes. Specifically IPv4.

Recently I've needed that functionality on Linux, as I have multiple old
>> systems that only understand classful, including the AT&T UnixPC (7300 or
>> 3B1). I suppose I should rewrite and open-source it.

> I /think/ (it's been too long since I've done this) that you would
> configure one classless interface with and another
> classless interface with -and- enable Proxy ARP on both
> (?) interfaces.  You will likely need to enter the target machine's IP
> addresses in a file that the Proxy ARP sub-system references to learn what
> target IPs that it needs to Proxy ARP for.

The point of bozo-arp and anyipd was that the only necessary configuration
was to turn it on. Of course, there may be scenarios in which one does not
want the router to respond to bogus ARP requests, in which case
bozo-arp/anyipd should not be used.

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