Subject: Re: PPP - address already in use
To: Jukka Marin <>
From: Julian Bean <>
List: current-users
Date: 03/20/1996 18:44:21
At 9:46 am 20/3/96, Jukka Marin wrote:
>> > Mar 19 08:23:41 muikku pppd[23397]: remote IP address
>> > Mar 19 08:23:41 muikku pppd[23397]: ioctl(SIOCAIFADDR): Address
>>already exists
>> > Mar 19 08:23:41 muikku pppd[23397]: add proxy arp entry: File exists
>> This is a nasty problem that has haunted us for a while now.  My
>> workaround is to publish permanent arp entries for all IPs that I do
>> proxy for, at boot time (I hacked /etc/netstart to do this).
>Yeah, I guess this would be a simple solution, but..
>How is the proxy arp system supposed to work? ;-)  I would think it was
>created for this kind of dynamic connections?  And now it seems it can't
>be used for PPP very well.

Dumb question:

Why proxy arp at all?  I have a small network (2 machines) hanging off a
PPP link.  It works fine with no proxy arp at all - machines in my bedroom
know to send all packets to the machine with the PPP link....

Maybe I'm missing something.  Yes, both sides of the PPP link are in the
same class C net and beyond that not subnetting is performed (i.e. netmask

Why does it work for me with no arp?  Is it because I only have a PPP
network, no ether involved?  Is it because I only have 2 machines.  A quick
diagram of my net:

        +--------------+        +---------------------+         +--------+
        |ISP's ethernet| ether  |ISP's terminal server| line    |Internet|
        |205.199.253.x |--------|        |---------|        |
        +--------------+        +---------------------+         +--------+
                                        | PPP over phone line
                                |My NetBSD machine|
                                |   |
                                        | PPP over serial cable
                                |My macintosh  |

Why would I need proxy arp?  If I put an ethernet on my NetBSD machine,
will I need it then?

As it is my mac uses as a default gateway.
has a route to (added automatically by pppd) and a default
route to (when it is logged on).

All the hosts in 205.199.253.x at the ISP use as their
default route.  And it all appears to work....


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